Range Plant Growth and Development

Range Plant Growth and Development
Photosynthesis Germination and Seedling Establishment Life Cycles and Phenology Secondary Compounds Seasonal Growth Rates You are here Seasonality and Life Cycles Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction Grazing Optimization This learning module covers the influence of grazing on plant productivity and development. Starting with the section on seasonality and life cycles you can progress to the morphology and development section, plant physiology section and finally to a section on grazing and plant growth. The material in this module is interconnected in many ways. While you can proceed through the material in the order presented, you can also jump forward to later information that is connected to the current subject, much as you can do in a Wiki. When we refer to plant physiology we are referring to how plants function. Subjects like germination, photosynthesis, respiration, and carbohydrate storage and allocation will be discussed. In our discussion of plant morphology we will cover plant anatomy at the tissue and whole plant scale. A discussion of buds or growing points and tillering is an important part of this section. While it is not our intent to teach a course in plant physiology or plant morphology, understanding certain aspects of physiology and morphology will help in understanding grazing effects. Range Plant Growth and Development

Seasonality and Life Cycles Terminology Life Cycles
Phenology Seasonal Growth Rates You are here Seasonality and Life Cycles Forage Quality Seasonality and Life Cycles Terminology Life Cycles Seasonal growth rates Forage Quality RDM RDM In this first section we will cover Seasonality and Life Cycles. First we will cover some common terms and then we will review the yearly life cycle and phenology of annual and perennial plants. At the end we will discuss seasonal growth rates, forage quality, and litter as it is related to the yearly life cycle.

Reading and references
Seasonality and Life Cycles Reading and references SEASONALITY & LIFE CYCLES Return to Course Map The Phenology Handbook, pg 1-15 George et al Annual Range Forage Production George and Bell Using Stage of Maturity…….. Reading references for the Seasonality and Life Cycles Section are provide on this slide with links to the references.

SEASONALITY & LIFE CYCLES
Plant Physiology Return to Course Map Terminology Life Cycles Forage Quality Seasonal growth rates RDM Let’s start with some terms.

Terminology Annual Perennial Seasonality and Life Cycles
Return to Course Map Annual Perennial In preparation to discuss annual and perennial plant life cycles we will define terms like annual, perennial, phenology, life cycle, grass, forb and shrub. An annual is a plant that starts from seed each year. A perennial is a plant that survives for several years. While perennial plants may produce seeds they invest a certain amount of energy to storing carbohydrates and surviving cold or dry periods.

Terminology Forb: dicot, non-woody Shrub
Seasonality and Life Cycles Terminology Return to Course Map Grass: monocot, most are not woody Forb: dicot, non-woody Grasses, or more technically graminoids, are monocotyledonous, usually herbaceous plants with narrow leaves growing from the base. Monocots are one of two major groups of flowering plants (angiosperms) that are traditionally recognized, the other being dicots. Monocot seedlings typically have one cotyledon (seed-leaf), in contrast to the two cotyledons typical of dicots. Graminoids include the "true grasses", of the Poaceae family, as well as the sedges of the Cyperaceae family and the rushes or Juncaceae family. The true grasses include cereals, bamboo, forages and turf grasses. Sedges include many wild marsh and grassland plants, and some cultivated ones such as water chestnut (Eleocharis dulcis) and papyrus sedge (Cyperus papyrus). Forbs are herbaceous flowering plants that are not grasses, sedges or rushes. Forbs are dicotyledonous and non-woody. The term, forb, is frequently used in vegetation ecology, especially in relation to grasslands. A shrub or bush is a horticultural rather than a strict botanical category of woody plant, distinguished from a tree by its multiple stems and lower height, usually less than 5–6 m (15–20 ft) tall. A large number of plants can be either shrubs or trees, depending on the growing conditions they experience. Shrub Dicot, woody

Seasonality and Life Cycles Terminology Return to Course Map PHENOLOGY is the science that measures the timing of life cycle events for plants, animals, and microbes, and detects how the environment influences the timing of those events. In the case of flowering plants, these life cycle events, include leaf budburst, first flower, last flower, first ripe fruit, seed set, leaf shedding, others. PHENOLOGY is the science that measures the timing of life cycle events for plants, animals, and microbes, and detects how the environment influences the timing of those events. In the case of flowering plants, these life cycle events, include leaf budburst, first flower, last flower, first ripe fruit, seed set, leaf shedding, others.

Plant Physiology Return to Course Map Terminology Life Cycles Forage Quality Seasonal growth rates RDM Now let’s look at the annual life cycles of annual and perennial plants.

Life cycles Seasonality and Life Cycles
Return to Course Map Plants must be adapted to seasonal changes in solar intensity, temperature, water availability, and day length. Many plants survive cold winters in a dormant state while others tolerate cold temperatures. These plants respond to warming temperatures and available moisture by initiating growth and proceeding through the growing season until cooling temperatures, day length or drying soil signal the beginning of dormancy. Some plants, must survive a dry season in a dormant state. These plants start to grow with the beginning of the rainy season proceeding through the growing season until drying soil signals the beginning of the dry season dormancy. Native perennial grasses and forbs in California’s foothill rangelands commonly enter a dormant or near dormant state during the dry season. Image courtesy of

Annual Life Cycles Annuals Germination Vegetative Flowering
Seasonality and Life Cycles Return to Course Map Annuals Germination Vegetative Seedling establishment Leaf growth Winter growth is slow Growth accelerates in spring Flowering Seed Set, Drying Dry and Die In California, foothill rangelands around the central valley and along the coast are dominated by introduced annual grasses and forbs. These foothill oak-woodland and valley grassland communities are often called annual rangelands. Each year most of the herbaceous plants in an annual dominated system are new. Following adequate fall rains seeds lying in the soil and in the litter at the soil's surface germinate and begin the new annual rangeland growing season. If rainfall continues to be adequate the new seedlings become established and grow by adding leaves. This is the vegetative phase of the annual life cycle. During the winter vegetative growth is slow. As temperatures warm in the spring growth accelerates and these annual plants begin a new phase where flower buds develop and elongate from near the soil surface until the flower becomes visible.

annual life cycle CALENDAR
Seasonality and Life Cycles Return to Course Map N D J F M A S O Germination & Seedling Establishment Slow Vegetative Growth Rapid Vegetative Growth Little or No Vegetative Growth Tiller Development Flowering Seed Development Seed Set Drying Stems & Leaves Dry & Dead Stems & Leaves Each year annual plants, germinate, become established and proceed through vegetative and reproductive stages. Seasonal growth rates are greatly influenced by the amount and timing of precipitation. During the winter when moisture is adequate but temperatures are low photosynthesis and plant growth are slow. With the arrival of warming spring temperatures, photosynthesis and plant growth rates increase. As soil moisture is depleted plants begin to dry and die becoming litter. We will cover photosynthesis, plant anatomy and growing points in a later section but if you want to jump to that material now use the links provided. Otherwise continue to the next slide. Timing of phenological events

Perennial Life Cycles Perennials Lives several years
Seasonality and Life Cycles Return to Course Map Perennials Lives several years Sexual reproduction Vegetative reproduction Stolons and Rhizomes Winter dormancy Dry season dormancy Vegetative phase Flowering Seed set and dispersal Dormancy Perennial plants live for several years. Therefore you will be managing the same plant year after year. Perennials re-grow each year. They reproduce from seed or vegetativly from tillers, stolons or rhizomes. Short lived perennials last 3-5 years whereas properly managed long-lived perennials can survive much longer. Woody perennials can live for decades and centuries. In temperate regions perennial plants must enter dormancy to survive freezing winter temperatures. In Mediterranean regions where there is a pronounced summer dry season perennial grasses and forbs may enter a dry season dormancy, regrowing with the fall rains. Much of the aboveground biomass of perennial grasses and forbs die as the cold or dry season approaches. The remainder of the aboveground and near surface portions of these plants enter a dormant phase until the cold or dry season is over. During cold dormancy (winter) soil moisture is stored during rainy periods and snow melt. As spring approaches these plants use this soil moisture to begin to grow as temperatures increase. These plants will remain vegetative for several weeks but will eventually flower and develop seeds. As the growing season progresses seed is set and eventually dispersed. With cooling temperatures the plants begin to enter dormancy and much of the aboveground biomass dies and dries. Most perennial grasses and forbs in the western U.S follow this winter dormancy life cycle pattern.

perennial life cycle CALENDAR
Seasonality and Life Cycles perennial life cycle CALENDAR Return to Course Map N D J F M A S O Dormant or Slow Vegetative Growth Rapid Vegetative Growth Slow Vegetative Growth Dormant Tiller Development Carbohydrate Use Carbohydrate Storage Apical Meristems Near Soil Surface Flower Stems Elongate Flowering Seed Development Seed Set Drying Stems & Leaves Dry & Dead Stems & Leaves This is an example of a life cycle calendar for a perennial grass in a temperate climate. Perennial plants live for several years. In most places in the temperate part of the world perennial grasses and forbs must survive cold periods in a dormant state. As spring temperatures increase perennial plants come out of dormancy and photosynthesis and growth begin slowly at first and faster as temperatures increase. Like annuals perennial plants go through vegetative and reproductive stages before the tops dry and die as the plant approaches the cold season and enters dormancy. We will cover photosynthesis, plant anatomy and growing points in a later section but if you want to jump to that material now use the links provided. Otherwise continue to the next slide. Timing of phenological events

Phenology and Life Cycles
Seasonality and Life Cycles Return to Course Map Phenology is the study of periodic plant life cycle events and how these are influenced by seasonal and interannual variations in climate. Examples include the date of germination or seedling emergence, or the date of flower or seed set. Forage quality changes as plants progress through their life cycle. This table is a list of 12 phenological stages or stages of maturity that are often used to describe the time of forage sampling for nutritional analysis or to describe the time of hay harvest. Phenological events

Plant Physiology Return to Course Map Terminology Life Cycles Forage Quality Seasonal growth rates RDM Forage quality changes as the plant progresses through its life cycle.

Phenology and forage quality
Seasonality and Life Cycles Phenology and forage quality Return to Course Map This graphic, based on data from oak woodlands in Madera County, shows the decline in crude protein with phenological stage or stage of maturity. Crude protein decreases in annual grasses with stage of maturity (see ANR Publications 8019 and 8022)

Plant Physiology Return to Course Map Terminology Life Cycles Forage Quality Seasonal growth rates RDM Seasonal growth rates change with changing temperature.

Seasonal growth rates Seasonality and Life Cycles
Return to Course Map D J F1 M A M1 Peak Growth rates in the annual rangelands following germination are rapid if temperatures are warm and slow if temperatures are cold. The average germination date at the UC Sierra Foothill Research and Extension Center in Yuba County is October 20 and the average standing crop is 347 lb/a or less than 12 percent of peak standing crop on December 1. During the winter growth is slow such that the average standing crop at UC SFREC on March 1 is only about 700 lb/a which is less than 25 percent of standing crop of 2942 lb/a on May 1. Thus in this example daily growth rates average about 5 lb/acre/day from October 20 to March 1. During rapid spring growth the average rates of growth are about 37 lb/acre/day resulting in an average standing crop on May 1 of 2942 lb/acre. On average, little production occurs during May at UC SFREC resulting in only small differences between average standing crop on May 1 and on average peak standing crop.

Seasonality and Life Cycles Seasonal growth rates Return to Course Map Growth rates of perennials in northeastern California On intermountain rangelands grass growth begins with warming temperatures following winter dormancy. For example, in northeastern California there is little or no grass production from October through February or March. Only about 10 percent of the annual production occurs in April as plants begin to grow. In May and June growth is rapid often accounting for 50 to 75 percent of the annual production. Growth slows for the rest of the summer with increasing temperatures in July.

Plant Physiology Return to Course Map Terminology Life Cycles Seasonal growth rates Forage Quality RDM At the end of each year grasses and forbs dry and become standing litter and eventually fall over or “lodge” to become horizontal litter that gradually decomposes.

Litter: Residual Dry matter
Seasonality and Life Cycles Litter: Residual Dry matter Return to Course Map Moderate grazing results in recommended RDM levels In California’s annual rangelands the grasses and forbs produced during the growing season dry and become litter as the growing season ends. We call this litter, residual dry matter or RDM. The University of California has published RDM guidelines for how much RDM should be left at the end of the grazing season for soil protection and to provide mulch to protect germinating seeds. Residual dry matter is covered in greater detail in Module 4, Presentation 2 of the Ecology and Management of Grazing online course. Heavy grazing results in low RDM levels Light grazing results in high RDM levels

Seasonality and Life Cycles Summary Return to Course Map In this section you have learned the differences between annual and perennial life cycles and how plant growth rates and forage quality change as range and pasture plants move through their life cycle. In this section you have learned the differences between annual and perennial life cycles and how plant growth rates and forage quality change as plants move through their life cycle. Now lets move on to plant morphology and how it interacts with grazing.

Photosynthesis Germination and Seedling Establishment Life Cycles and Phenology Secondary Compounds Seasonal Growth Rates You are here Seasonality and Life Cycles Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction Grazing Optimization In this next section we will cover plant morphology and development. Range Plant Growth and Development

Morphology Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction
Morphology and Development Shrub Anatomy Reproduction In our discussion of plant morphology we will cover plant anatomy at the tissue and whole plant scale. A discussion of buds or growing points is an important part of this section. You will learn about vegetative reproduction in the form of stolons and rhizomes and tillers and you will learn about reproduction and flowering. You are here

MORPHOLOGY Briske, Chp 4. Dev. Morph and Phys of Grasses. Introduction and Developmental Morphology Sections. Skinner and Moore. Growth and Dev of Forage Plants How Grass Grows Reading references for the Morphology Section are provide on this slide with links to the references.

morphology Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction
Plant Physiology Return to Course Map Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction Let’s start with a section on grass anatomy.

Grass Anatomy Please review “How Grass Grows” at the link below.
Morphology and Development Grass Anatomy Return to Course Map Please review “How Grass Grows” at the link below. Overview of the Grass Plant Shoot Development Crown Leaf Formation Leaf Expansion Dynamics Tillering Rhizome and Stolon Development Flowering Root Development Germination Process Seasonal Development Select the link below to get an overview of grass anatomy and how grass grows. Pay close attention to the sections on shoot development, crown, leaf formation, leaf expansion dynamics, tillering, rhizome and stolon development and flowering. Also review the sections on root development, germination and seasonal development.

Growing Points Apical meristems (flower)
Morphology and Development Growing Points Return to Course Map Apical meristems (flower) Axillary buds (give rise to tillers, rhizomes and stolons) Intercalary meristems or collar (leaf expansion) Some growing points become elevated as the growing season progresses. Buds near the ground are less likely to be grazed Delaying bud elevation reduces risk of bud removal by grazing There are several growing points on a grass plant. Apical meristems or buds develop into the flower and are elevated during the flowering process. Axillary buds give rise to tillers, rhizomes and stolons.

Morphology and Development Growing Points Return to Course Map Apical meristems (flower) Axillary buds (give rise to tillers, rhizomes and stolons) Intercalary meristems or collar (leaf expansion) Some growing points become elevated as the growing season progresses. Buds near the ground are less likely to be grazed Delaying bud elevation reduces risk of bud removal by grazing Intercalary meristems allow leaves to expand following grazing or mowing.

Morphology and Development Growing Points Return to Course Map Apical meristems (flower) Axillary buds (give rise to tillers, rhizomes and stolons) Intercalary meristems or collar (leaf expansion) Some growing points become elevated as the growing season progresses. Buds near the ground are less likely to be grazed Delaying bud elevation reduces risk of bud removal by grazing Buds near the ground are less likely to be grazed or mowed but some buds become elevated as the season progresses increasing the risk of removal during grazing or mowing.

Morphology and Development Growing Points Return to Course Map Apical meristems (flower) Axillary buds (give rise to tillers, rhizomes and stolons) Intercalary meristems or collar (leaf expansion) Some growing points become elevated as the growing season progresses. Buds near the ground are less likely to be grazed Delaying bud elevation reduces risk of bud removal by grazing Apical meristem rising Delaying bud elevation reduces risk of bud removal.

Morphology and Development Vegetative Phase Return to Course Map In the vegetative phase, shoots consist predominantly of leaf blades. Leaf blade collars remain nested in the base of the shoot and there is no evidence of sheath elongation or culm development. Grasses and other plants progress through a vegetative phase, a transition phase and a reproduction phase. In the vegetative phase shoots are mostly leaf. Leaf blade collars remain nested in the base of the shoot and there is no evidence of sheath elongation or culm development.

Elongation (Transition) Phase
Morphology and Development Elongation (Transition) Phase Return to Course Map Floral induction - Apical meristems is gradually converted from a vegetative bud to a floral bud. During the transition phase, leaf sheaths begin to elongate, raising the meristematic collar zone to a grazable height. Culm internodes also begin elongation in an "un-telescoping" manner beginning with the lowermost internode thereby raising the meristematic zone (floral bud and leaf bases) to a vulnerable position. In response to daylength, temperature or other environmental variables the apical meristem is gradually converted from a vegetative bud to a floral bud. This is called floral induction. This conversion phase is termed the transition phase. During the transition or elongation phase floral induction begins, leaf sheaths begin to elongate and culm internodes also elongate raising the floral bud and leaf bases to a grazable height.

Morphology and Development Reproductive Phase Return to Course Map The flowering phase begins with the conversion from vegetative to floral bud. Much of this is unseen until the emergence of the seed head from the sheath of the flag leaf (boot stage). Within a few days, individual florets within the seed head are ready for pollination. During the reproductive phase the conversion from vegetative to floral bud is completed and the unseen flower emerges from the leaf sheath. Just before the flower emerges it is covered by the leaf sheath and this is commonly called the “boot stage” of development. Successful regrowth following defoliation depends on productive plant meristems or buds. Plant species with growing points elevated are more susceptible to grazing than plants that keep their growing points close to the ground during most of their life cycle. Apical meristem rising

Plant Physiology Return to Course Map Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction Forb anatomy differs from grass anatomy.

Forb anatomy Morphology and Development
Return to Course Map Forb anatomy varies between species. This diagram of several legumes identifies some common forb plant parts including leaves, stems, nodes, internodes, stolons and roots.

Forb growing points Morphology and Development
Return to Course Map Growing point or apical bud Like grasses and other plants, forbs have apical buds that may develop into flowers and axillary buds that produce stems, rhizomes and stolons.

Plant Physiology Return to Course Map Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction Shrub anatomy includes some extra growing points.

Shrub Anatomy Coast live oak resprouts Chamise resprouts
Morphology and Development Shrub Anatomy Return to Course Map Coast live oak resprouts Chamise resprouts Woody plants have apical and axillary buds like those of non-woody forbs. They also have buds on the root crown or roots that resprout following damage or loss of the aboveground stems as occurs during fire or following wood cutting. Chamise and some oaks are strong resprouters following fire.

Plant Physiology Return to Course Map Grass Anatomy Forb Anatomy Shrub Anatomy Reproduction In this section sexual and asexual plant reproduction will be covered.

Reproduction Long Day Plants Short Day Plants
Morphology and Development Reproduction Return to Course Map Long Day Plants Short Day Plants Sexual Reproduction (flowers and seeds) Vegetative Reproduction (stolons, rhizomes) In grasses and forbs some apical buds produce flowers during the reproductive stage of development. The reproductive or flowering stage of growth is triggered primarily by photoperiod but can be slightly modified by temperature and precipitation. Some plants can be classified as long day plants and others as short day plants on the basis of their flowering date. Not all range plants reproduce by way of flowers and seed which is known as sexual reproduction. Many grasses reproduce vegetatively or asexually by way of tillers, stolons and rhizomes that give rise to new plants. Additionally many woody plants reproduce vegetativly via resprouts from the root crown or roots. (Roberts 1939, Leopold and Kriedemann 1975, Dahl 1995)

Reproduction - LONG DAY PLANTS
Morphology and Development LONG DAY PLANTS Return to Course Map Some plants are long-day plants and others are short-day plants. The long-day plants reach the flowering phenological stage after exposure to a critical photoperiod and during the period of increasing daylight between mid April and mid June. Generally, most cool-season plants with the C3 photosynthetic pathway are long-day plants and reach flower phenophase before 21 June. Some plants are long-day plants and others are short-day plants. The long-day plants reach the flowering stage after exposure to a critical photoperiod and during the period of increasing daylight between mid April and mid June. Generally, most cool-season plants with the C3 photosynthetic pathway are long-day plants and reach the flower phenophase before 21 June. Photosynthetic pathways will be discussed in the next section.

Morphology and Development Reproduction short Day Plants Return to Course Map Short-day plants are induced into flowering by day lengths that are shorter than a critical length and that occur during the period of decreasing day length after mid June. Short-day plants are technically responding to the increase in the length of the night period rather than to the decrease in day length. Generally, most warm-season plants with the C4 photosynthetic pathway are short-day plants and reach flower phenophase after 21 June. The annual pattern in the change in daylight duration follows the calendar and is the same every year for each region. Short-day plants are induced into flowering by day lengths that are shorter than a critical length and that occur during the period of decreasing day length after late June. Short-day plants are technically responding to the increase in the length of the night period rather than the decrease in day length. Generally, most warm-season plants with the C4 photosynthetic pathway are short-day plants and reach the flower phenophase after 21 June. The annual pattern in the change in daylight duration follows the calendar and is the same every year for each region. (Weier et al. 1974, Leopold and Kriedemann 1975).

Morphology and Development Reproduction Return to Course Map Plant populations persist through both asexual (vegetative) reproduction and sexual reproduction. The frequency of true seedlings produced from seed is low in established grasslands and occurs only during years with favorable moisture and temperature conditions in areas of reduced competition from older tillers, and when resources are easily available to the growing seedling. Plant populations persist through both asexual (vegetative) reproduction and sexual reproduction (Briske and Richards 1995). The frequency of true seedlings produced from seed is low in established grasslands and occurs only during years with favorable moisture and temperature conditions in areas of reduced competition from older tillers, and when resources are easily available to the growing seedling. (Wilson and Briske 1979, Briske and Richards 1995),

Morphology and Development Reproduction SEXUAL Return to Course Map Sexual reproduction is necessary for a population to maintain the genetic diversity enabling it to withstand large-scale changes. However, production of viable seed each year is not necessary to the perpetuation of a healthy grassland. Sexual reproduction is necessary for a population to maintain the genetic diversity enabling it to withstand large-scale changes. However, production of viable seed each year is not necessary to the perpetuation of a healthy grassland. (Briske and Richards 1995).

Morphology and Development Reproduction SEXUAL Return to Course Map Reproductive shoots are adapted for seed production rather than for tolerance to defoliation Grass species that produce a high proportion of reproductive shoots are less resistant to grazing than are those species in which a high proportion of the shoots remains vegetative. Reproductive shoots are adapted for seed production rather than for tolerance to defoliation . Grass species that produce a high proportion of reproductive shoots are less resistant to grazing than are those species in which a high proportion of the shoots remains vegetative.

Reproduction Morphology and Development ASEXUAL OR VEGETATIVE Return to Course Map Vegetative growth is the dominant form of reproduction in semiarid and mesic grasslands Annual plants are dependent on seed production each year for survival. Short-lived perennials depend on seed production. Long-lived perennials rely more on vegetative reproduction. A common growth characteristic of perennial grass plants is their ability to spread vegetatively from a parent plant. Vegetative growth is the dominant form of reproduction in semiarid and mesic grasslands, including the tallgrass, midgrass, and shortgrass prairies of North America. Tillers, stolons and rhizomes allow grasses to spread vegetatively. While annual plants and short-lived perennials are dependent on production of seed for survivial, long-lived perennials rely on tillers, stolons and rhizomes to reproduce asexually.

tillering Morphology and Development
A tiller is a stem, produced at the base of grass plants. Tillers are segmented, each segment possessing its own two-part leaf. They are involved in vegetative propagation. Tillering is a property possessed by many species in the grass family which enables them to produce multiple stems (tillers) starting from the initial single seedling. This ensures the formation of dense tufts and multiple seed heads. Tillering rates are heavily influenced by soil water status. When soil moisture is low tillering is inhibited. New tillers arise from axillary buds. Tiller density is controlled by the rate of recruitment of new tillers and the mortality of existing tillers. Often, there is high tiller mortality coinciding with flowering in perennial grasses. In a smooth bromegrass sward, tiller density was highest in early spring and decreased as spring growth progressed. Tiller recruitment in perennial cool-season grasses such as smooth bromegrass involves at least two tiller generations annually, with tillering episodes occurring in early spring and immediately following flowering. Grazing or mowing, nitrogen fertilization, soil moisture and sunlight stimulate tillering. Shade, soil moisture deficits and poor fertility inhibit tillering.

Reproduction Bunch grasses spread by the production of tillers.
Morphology and Development ASEXUAL OR VEGETATIVE Return to Course Map Bunch grasses spread by the production of tillers. Stoloniferous grasses spread by lateral stems, called stolons, that creep over the ground and give rise to new shoots periodically along the length of the stolon. Rhizomatous grasses spread from below ground stems known as rhizomes. Grasses are often classified as bunch, stoloniferous or rhizomatous referring to their vegetative growth habit. Bunch grasses spread by the production of tillers. Tillers originate from the crown area and grow upward from the base of the plant. It is this type of continuous shoot production by means of tillers that gives the plant a clumpy appearance; hence the name bunch grass. Stoloniferous grasses spread by lateral stems, called stolons, that creep over the ground and give rise to new shoots along the length of the stolon. Lawns formed from stoloniferous grasses appear to have their aerial shoots growing laterally along the ground rather than upright as in bunch or rhizomatous grasses. Creeping bentgrass is a good example of this type of growth. Rhizomatous grasses spread from below ground stems known as rhizomes. These rhizomes terminate in a shoot that emerges some distance from the mother plant. As these new shoots mature they will also produce rhizomes that eventually produce new shoots thus spreading the plant into adjacent areas. Root growth also originates at the crown. However, roots continue to lengthen and grow from the root tip as opposed to the growth of shoots and leaves which are pushed upward and outward from the crown at the base of the plant. Roots are naturally sloughed-off and new ones regrow as a normal part of grass plant growth. Also, adverse environmental conditions can significantly shorten the life of grass plant roots. For example, weather and soil stresses associated with drought conditions or excessive rainfall can cause significant root injury or loss and inhibit growth.

Morphology and Development Summary Return to Course Map . In this section you learned about plant growing points, how plants grow, phases of plant growth and reproduction. You learned that vegetative reproduction in the form of tillers, stolons and rhizomes are more important than reproduction via seeds in most grasslands. You also learned that buds close to the ground are less vulnerable to grazing than when they are elevated. In this section you learned about plant growing points, how plants grow, phases of plant growth and reproduction. You learned that vegetative reproduction in the form of tillers, stolons and rhizomes are more important than reproduction via seeds in most grasslands. You also learned that buds close to the ground are less vulnerable to grazing than when they are elevated.

Photosynthesis Germination and Seedling Establishment Life Cycles and Phenology Secondary Compounds Seasonal Growth Rates You are here Seasonality and Life Cycles Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction Grazing Optimization Now we will move on to the section on plant physiology. Range Plant Growth and Development

Germination & Seedling Establishment
Photosynthesis Germination and Seedling Establishment Plant Physiology Germination & Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Secondary Compounds Plant Physiology Water and Nutrients Carbohydrates and Allocation When we refer to plant physiology we are referring to how plants function. Subjects like germination, photosynthesis, respiration, and carbohydrate storage and allocation will be discussed. While it is not our intent to teach a course in plant physiology understanding certain aspects of physiology will help in understanding grazing effects.

Plant physiology McKell, C.M Morphogenesis and management of annual range plants in the United States. Pg Briske, Chp 4. Dev. Morph and Phys of Grasses. Grazing Resistance Section. Waller and Lewis Occurrence of C3 and C4 photosynthetic pathways in North American grasses. Carbohydrate Reserves: What you learned may be wrong. Reading references for the Plant Physiology Section are provide on this slide with links to the references.

Plant physiology Germination and Seedling Establishment Photosynthesis
Return to Course Map Germination and Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Most plants start there lives with germination of a seed and seedling establishment.

Plant Physiology Germination & Seedling Establishment Return to Course Map Let’s begin the plant physiology section with an overview of germination and seedling establishment. Seed germination initiates a series of changes that ultimately lead to a mature plant and reproduction of the species once again. Favorable temperature and moisture are essential for successful development of the seedling during the first critical stages of growth. Rapid germination and growth results in a high demand for light, moisture, nutrients and other plant growth requirements.

Plant Physiology Germination & Seedling Establishment Return to Course Map Seed Coat See Anatomy Embryo Endosperm (food reserves) Seed coat (pericarp) Variable seed production Empty seeds All fully developed seeds contain an embryo and, in most plant species food reserves, wrapped in a seed coat. Some plants produce varying numbers of seeds that lack embryos, these are called empty seeds, and never germinate. Under favorable conditions, the seed germinates and develops a seedling. Empty Seeds

Plant Physiology Germination & Seedling Establishment Return to Course Map While water is required, temperature, oxygen and light quality may also influence germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the dry weight of the seed, before cellular metabolism and growth can begin. The uptake of water by seeds is called imbibition, which leads to the swelling and the breaking of the seed coat. When seeds are formed, most plants store food reserves with the seed, such as starch, proteins, or oils. This food reserve provides nourishment to the growing embryo. When the seed imbibes water, hydrolytic enzymes are activated which break down these stored food resources into metabolically useful chemicals. After the seedling emerges from the seed coat and starts growing roots and leaves, the seedling's food reserves are typically exhausted; at this point photosynthesis provides the energy needed for continued growth and the seedling now requires a continuous supply of water, nutrients, and light.

Phototropism Plant Physiology
Return to Course Map When a seed germinates the new seedling grows toward light this is called phototropism.

Plant Physiology Germination & Seedling Establishment Oxygen is required for respiration during germination. Oxygen is found in soil pore spaces but if a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen starved. Some seeds have impermeable seed coats sometimes called hard seed. Hard seed is common in legumes Return to Course Map Oxygen is required for respiration during germination. Oxygen is found in soil pore spaces but if a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen starved. Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment. Hard seed in rose clover can allow seed to survive in soil for more than 20 years.

Plant Physiology Germination & Seedling Establishment Return to Course Map Temperature also influences germination. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Temperature also influences germination. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above room-temperature F (16-24 C), while others germinate just above freezing and others germinate only in response to alternations in temperature between warm and cool. Some seeds germinate when the soil is cool F ( C), and some when the soil is warm F (24-32 C).

Plant Physiology Germination & Seedling Establishment Return to Course Map Some seeds require exposure to cold temperatures (vernalization) to break dormancy. Seeds in a dormant state will not germinate even if conditions are favorable. Some seeds will only germinate following hot weather and others exposed to hot temperatures during a forest fire which cracks their seed coats. Some seeds need to pass through an animal's digestive tract to weaken the seed coat enough to allow the seedling to emerge. Some seeds require exposure to cold temperatures (vernalization) to break dormancy. Seeds in a dormant state will not germinate even if conditions are favorable. Some seeds will only germinate following hot weather and others exposed to hot temperatures during a forest fire which cracks their seed coats. Smoke has also been shown to stimulate germination of some plant species. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for growth of the seedling. Some seeds need to pass through an animal's digestive tract to weaken the seed coat enough to allow the seedling to emerge.

Plant Physiology Germination & Seedling Establishment Return to Course Map Variability in the rate of germination exists between and within species. Seed size has been shown to be a critical factor in promoting seedling vigor. In legumes and other forbs, seed coat hardness or impermeability often retards germination but spreads germination over years which is a survival advantage for the species. Variability in the rate of germination exists between and within species. Seed size has been shown to be a critical factor in promoting seedling vigor. In legumes and other forbs, seed coat hardness or impermeability often retards germination but spreads germination over years which is a survival advantage for the species. In general, germination is reduced with increasing age of seeds.

Plant Physiology Germination & Seedling Establishment Return to Course Map On annual rangelands estimates of germinable seed exceed 20,000 per m2. On annual rangelands the number of plants early in the growing season has been reported to vary from 20 to nearly 100 per square inch. Considerable reduction in this number takes place as the season progresses. The lost seedlings decay and provide a flush of nutrients early in the growing season. On annual rangelands estimates of germinable seed exceed 20,000 per m2. A high proportion of the seeds are at or above the soil surface in litter. This placement exposes a large proportion of the seedbank to predation and wide variability in moisture and temperature on a diurnal and seasonal basis. The number of plants early in the growing season has been reported to vary from 20 to nearly 100 per square inch. Considerable reduction in this number takes place as the season progresses. The lost seedlings decay and provide a flush of nutrients early in the growing season.

Plant Physiology Germination & Seedling Establishment Return to Course Map Rapid root growth is fundamental to establishment and development of annual rangeland plants. Individual plants and species may gain an advantage over competitors if they exhibit rapid root growth and are able to maintain both rapid root and top growth. Annual grasses frequently exhibit root growth rates greater than native perennial grasses Annual grass (cheatgrass) roots (b) grew faster in this study than blue bunch wheatgrass (native perennial ) roots (a) (Harris 1977, JRM) Rapid root growth is fundamental to establishment and development of annual rangeland plants. Individual plants and species may gain an advantage over competitors if they exhibit rapid root growth and are able to maintain both rapid root and top growth. In California, annual grasses frequently exhibit root growth rates greater than native perennial grasses. This is one of the reasons that native perennial grass establishment is so difficult in California’s annual rangelands.

Return to Course Map Germination and Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Now we begin a long section on photosynthesis.

CO2 + H2O CH2O + O2 Photosynthesis Plant Physiology Sunlight
Return to Course Map CO2 + H2O CH2O + O2 Sunlight Chlorophyll In the presence of sunlight and chlorophyll, photosynthesis is a biochemical process that converts carbon dioxide and water to carbohydrates and oxygen. You may see this formula written in various ways. CH2O is a short hand for sugar or carbohydrate, C6H12O6 is more correct.

Four Fundamental Concepts
Plant Physiology Four Fundamental Concepts Return to Course Map Plants are the only source of energy for grazing animals. The formation of sugars, starches, proteins and other foods is dependent on photosynthesis. Plants do not get food from the soil. They obtain raw materials needed for photosynthesis and subsequent food production When leaves are removed from plants, food-producing capacity is reduced. When considering grazing and plants it is important to remember that 1) Plants are the only source of energy for grazing animals, 2) the formation of sugars, starches, proteins and other foods is dependent on photosynthesis, 3) plants do not get food from the soil. They obtain raw materials needed for photosynthesis and subsequent food production, and 4) when leaves are removed from plants, food-producing capacity is reduced.

photosynthesis Plant Physiology To learn more about Photosynthesis:
Return to Course Map To learn more about Photosynthesis: Photosynthesis is the bonding together of CO2 (carbon dioxide) with H2O (water) to make CH2O (sugar) and O2 (oxygen), using the sun's energy. The sugar contains the stored energy and serves as the raw material from which other compounds are made. Respiration is the reverse of photosynthesis. It releases stored energy in sugar in the presence of oxygen, and this reaction releases the CO2 and H2O originally bonded together during photosynthesis. 68

Photosynthetic rate Factors that influence photosynthetic rate
Plant Physiology Photosynthetic rate Return to Course Map Numerous factors influence photosynthesis including leaf area, light intensity and quality, carbon dioxide content of the air, physiological efficiency, soil nutrients, water supply and temperature. Physiological efficiency Soil nutrients Water supply Temperature Factors that influence photosynthetic rate Leaf area Light intensity and quality CO2 content of the air

Leaf area and light intensity
Plant Physiology Leaf area and light intensity Return to Course Map Light interception by plants increases with leaf area. Relationship between light interception and leaf area (Brougham 1956)

Photosynthesis & light intensity
Plant Physiology Photosynthesis & light intensity Return to Course Map Lightly grazed Closely grazed Photosynthesis increases with increasing light intensity. This graph shows the response of gross photosynthesis to light intensity for a closely grazed sward (LAI = 1) and a lightly grazed sward (LAI = 3). 71

Photosynthesis & leaf area
Plant Physiology Photosynthesis & leaf area Return to Course Map Thus photosynthesis increases with increasing leaf area. (Parsons et al ) 72

Production & leaf area Plant Physiology
Return to Course Map And it follows that forage yield resulting from photosynthesis increases with leaf area up to a point. At some point, often around a Leaf Area of 4 or 5 for pasture, production slows because lower leaves are shaded by upper leaves. Relationship between leaf area and herbage yield (Brougham 1956)

GROSS & NET PRIMARY PRODUCTION
Plant Physiology GROSS & NET PRIMARY PRODUCTION Return to Course Map NPP=GPP - R GPP and NPP increase as leaves are added until upper leaves begin shading lower leaves then R increases resulting in decrease in NPP Production resulting from photosynthesis is expressed as gross primary production (GPP) and net primary production (NPP). NPP is GPP minus respiration (R). GPP and NPP initially increase as leaf area increases but as upper leaves begin to shade lower leaves respiration increases resulting in a decrease in NPP. Thus production of biomass begins to decrease. 74

STOMATES AND WATER RELATIONS
Plant Physiology STOMATES AND WATER RELATIONS Return to Course Map Stomate Photosynthesis is also influenced by plant water relations. The roots of plants take water from the soil and loose water through stomates in the leaves. Stomates are the "pores" in leaves (and stems) through which CO2 is taken in and O2 is released during photosynthesis. Plants control when stomata are open or closed and the width of the opening . The width of the opening is controlled by two guard cells that expand and contract to open and close the space between them. Transpiration is the water that evaporates out of stomates when they are open. This pulls more water and nutrients up to the top of the plant, but causes the plant to lose water and potentially dehydrate. Water Use Efficiency (WUE) refers to how good the plant is at bringing in carbon dioxide for photosynthesis without losing much water out of its stomata. More specifically, WUE is the ratio of carbon dioxide intake to water lost through transpiration. Guard Cells

Water relations Water required for photosynthesis
Plant Physiology Water relations Return to Course Map Water required for photosynthesis Lost through stomates (transpiration) Arid and semi-arid lands frequently subjected to water stress Drought tolerant Moisture stress occurs when the water in a plant's cells is reduced to lower than normal levels. This can occur because of a lack of water in the plant's root zone, higher rates of transpiration than the rate of moisture uptake by the roots, or because of an inability to absorb water due to a high salt content in the soil water. Image courtesy of uwstudentweb.uwyo.edu/d/dbrouss1/stomate.htm home.howstuffworks.com/prickly-pear-cactus.htm 76

PHOTOSYNTHETIC PATHWAYS
Plant Physiology PHOTOSYNTHETIC PATHWAYS C3, C4 & CAM Pathways Return to Course Map There are three types of photosynthesis : C3, C4, and CAM. C3 photosynthesis is the type that most plants use and that everyone learns about in school (it was all we knew about until a few decades ago). C4 and CAM photosynthesis are both adaptations to arid conditions because they result in better water use efficiency. In addition, CAM plants can "idle," saving precious energy and water during harsh times, and C4 plants can photosynthesize faster under the desert's high heat and light conditions than C3 plants because they use an extra biochemical pathway and special anatomy to reduce photorespiration. 77

Plant Physiology C3 photosynthesis Return to Course Map C3 because CO2 is first incorporated into a 3-carbon compound. Stomata are open during the day. Photosynthesis takes place throughout the leaf. Adaptive Value: more efficient than C4 and CAM plants under cool and moist conditions and, under normal light conditions. Most plants are C3. Plants are classified as C3 because CO2 fixed during photosynthesis is first incorporated into a 3-carbon compound. Stomates are open during the day. Photosynthesis takes place throughout the leaf. The Adaptive Value of C3 photosynthesis is that it is more efficient than C4 and CAM photosynthesis under cool and moist conditions and under normal light intensities. Most plants are C3 plants. 78

C4 photosynthesis CO2 is first incorporated into a 4-carbon compound
Plant Physiology C4 photosynthesis Return to Course Map CO2 is first incorporated into a 4-carbon compound Stomata are open during the day. Photosynthesis takes place in inner bundle sheath cells Adaptive Value: Photosynthesizes faster than C3 plants under high light intensity and high temperatures. Better water use efficiency than C3 because CO2 uptake is faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis C4 plants include several thousand species in at least 19 plant families Examples: fourwing saltbush, corn, and many summer annual plants In C4 photosynthesis CO2 is first incorporated into a 4-carbon compound. Stomata are open during the day. Photosynthesis takes place in the inner bundle sheath cells Adaptive Value: Photosynthesizes faster than C3 plants under high light intensity and high temperatures. Has better Water Use Efficiency because CO2 uptake is faster and so does not need to keep stomata open as much (less water lost by transpiration) for the same amount of CO2 gain for photosynthesis. C4 plants include several thousand species in at least 19 plant families. Examples: fourwing saltbush, corn, and many of our summer annual plants. 79

Cam photosynthesis Crassulacean Acid Metabolism (CAM)
Plant Physiology Cam photosynthesis Return to Course Map Crassulacean Acid Metabolism (CAM) Stomata open at night and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released for photosynthesis Adaptive Value: Better Water Use Efficiency than C3 plants CAM-Idle When conditions are extremely arid, CAM plants can just leave their stomata closed night and day. CAM plants include many succulents such as cactuses and agaves and also some orchids and bromeliads Next is CAM photosynthesis. CAM stands for Crassulacean Acid Metabolism. Crassulaceaen is after the Crassulaceae family in which CAM Ps was first found and acid because CO2 is stored in the form of an acid before use in photosynthesis. In CAM plants stomates open at night, when evaporation rates are usually lower, and are usually closed during the day. The CO2 is converted to an acid and stored during the night. During the day, the acid is broken down and the CO2 is released for photosynthesis . CAM photosynthesis has adaptive value. Because the stomates are closed during the day CAM photosynthesis provides for better water use efficiency than C3 plants under arid conditions. CAM plants may idle when conditions are extremely arid. This is sometimes called CAM-idle. Under CAM-idle plants can leave their stomates closed night and day. Oxygen given off in photosynthesis is used for respiration and CO2 given off in respiration is used for photosynthesis. This is a little like a perpetual energy machine, but there are costs associated with running the machinery for respiration and photosynthesis so the plant cannot CAM-idle forever. But CAM-idling does allow the plant to survive dry spells, and it allows the plant to recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells). CAM plants include many succulents such as cactus and agaves and also some orchids and bromeliads. 80

Cool & warm season grasses
Plant Physiology Cool & warm season grasses Return to Course Map Most of the plants that we call cool season plants are classified as C3 plants. Warm season grasses are classified as C4 plants. (See Waller, S.S. and J.K. Lewis Occurrence of C3 and C4 Photosynthetic Pathways in North American Grasses. Journal of Range Management 32:12-28 for an review and list of C3 and C4 range plants). Waller, S.S. and J.K. Lewis Occurrence of C3 and C4 Photosynthetic Pathways in North American Grasses. Journal of Range Management 32:12-28 for an review and list of C3 and C4 range plants. 81

Root growth temperatures
Plant Physiology Root growth temperatures Return to Course Map The optimum soil temperatures for root growth in C3 grasses is 55 to 65 F and for C4 grasses F. 82

Water use efficiencies
Plant Physiology Water use efficiencies C3 VS C4 Return to Course Map C3 grasses must have their stomates open longer than C4 to capture the same amount of CO2 Open stomates lose more water. C4 grasses use less water per unit of CO2 fixed. C3 grasses are more easily drought stressed during warm weather. 83

CO2 CONCENTRATION Plant Physiology
Return to Course Map Photosynthetic rate (Y axis) increases as atmospheric CO2 increases. At current atmospheric CO2 concentrations the photosynthetic rate of C4 plants is slightly above that of C3 plants (left vertical dashed line). If CO2 concentration were to double as some global change models predict then photosynthetic rate of C3 plants would be greater than C4 plants.

Light, Temperature and CO2
Plant Physiology Light, Temperature and CO2 C3 VS C4: Return to Course Map Comparison of CO2 Fixation by two Atriplex Species. Atriplex patula is a C3 plant, while Atriplex rosea is a C4 plant. The C4 species performs better under high light intensity, high leaf temperature and high carbon dioxide concentration. 85

Germination and Seedling Establishment Photosynthesis
Plant Physiology Plant physiology Return to Course Map Germination and Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Carbohydrates stored in roots and stems are the "savings account" of many forage plants. They are energy stores used for winter survival and regrowth after defoliation. In this section you will learn about carbohydrate storage and movement of carbohydrates within the plant.

Reduced carbohydrate storage
Plant Physiology Reduced carbohydrate storage Return to Course Map Carbohydrates are the plant’s energy source Energy needed for: Root replacement Leaf and stem growth following dormancy Respiration during dormancy Bud formation Regrowth following top removal Sugars produced during photosynthesis are used as an energy source immediately or stored or converted to starch and then stored. These stored carbohydrates are an energy source that the plant can draw on when photosynthesis is inadequate to meet current plant energy needs. Dormancy is one period when photosynthesis is low or nonexistent. Thus the plant draws on these reserves to start growth as dormancy ends. The plant uses this energy for such activities as 1) root replacement, 2) leaf and stem growth following dormancy, 3) respiration during dormancy, 4) bud formation and 5) regrowth following top removal. 87

Carbon distribution/allocation
Plant Physiology Carbon distribution/allocation Return to Course Map Plant scientists use the term ‘source’ where carbohydrate is produced and ‘sink’ where carbohydrate is utilized. Plant organs can be either sources or sinks depending on stage of growth and environmental conditions. 88

Plant Physiology Carbon distribution/allocation Return to Course Map In early spring, carbohydrates stored in seed, crown, stem base, root or rhizome tissues are the source for carbon and energy utilized in the formation of the first new leaves; which in this case are the sink. When enough leaf area has formed such that the surface area has sufficient photosynthetic capacity to produce more carbohydrate that required for growth, that leaf then becomes a source of sugar. Once the leaf is fully extended, it is no longer a sink for growth. 89

Plant Physiology Carbon distribution/allocation Return to Course Map Thereafter, sugars produced in excess of respiratory needs are available for translocation to sinks in other parts of the plant. Meristematic tissues, which are undifferentiated growth points throughout a plant, have priority for allocation of non-structural carbohydrate. The sink for excess non-structural carbohydrate might be new leaf, tiller, root, stem or seed production. During the stem elongation phase, the developing reproductive organs inside the stem are the sink. During seed filling, the stem is then the source and the seed is the sink. If adverse conditions limit seed filling, excess sugars may be leftover in the stem. High respiratory rates in cool season grasses during hot weather may become a sink, burning up sugars that might otherwise go towards growth or seed production. When growth slows or stops due to cold temperatures, lack of water or other nutrients, the sink is removed. As long as there is still green leaf tissue and adequate sunlight to allow production of photosynthates, accumulation may occur whenever carbohydrate production exceeds utilization. 90

Plant Physiology Carbon distribution/allocation Return to Course Map The source-sink relationship between various plant organs is very dynamic, and can change hourly as environmental conditions affect photosynthetic capacity, respiration, and growth. Polysaccharides are too large for transport, so they are hydrolyzed to sugars for translocation. Much of the translocation of sugars from source to sink occurs in stem tissue. This is why stems are often higher in sugar concentration than leaves. 91

Return to Course Map Germination and Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds In this section we will briefly cover water and nutrient movement in plants.

Water and Nutrient uptake
Plant Physiology Water and Nutrient uptake Return to Course Map For more information on plant water movement see these two videos: Roots take up water and nutrients from the soil.

Available water Plant Physiology
Return to Course Map When soil water content exceeds the permanent wilting point water is available to plants. In crop plants permanent wilting point is about 15 atm of pressure. However, many arid land plants can extract soil water well below the permanent wilting point for crop plants. Field capacity is the amount of soil water left after gravitational drainage of water from the soil.

Nutrient uptake Plant Physiology
Return to Course Map Plants use inorganic minerals for nutrition. Complex interactions involving decomposition of rocks, organic matter, animals and microbes take place to form inorganic nutrient ions in soil water. Roots absorb these mineral ions if they are readily available. They can be tied up by other elements or by alkaline or acidic soils. Soil microbes also assist in ion uptake.

Mycorrhizae Plant Physiology
Return to Course Map Mycorrhizae are a mutualism between plants and fungi. The plant provides the fungus with carbohydrates and the fungus helps the plant get nutrients from the soil, like nitrogen. Plants make carbohydrates from carbon dioxide and sunlight and their growth is usually limited by nitrogen. While fungi can absorb nitrogen and phosphorus from the soil, they can’t make their own carbohydrates.

Germination and Seedling Establishment Photosynthesis
Plant Physiology Plant physiology Return to Course Map Germination and Seedling Establishment Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Besides producing carbohydrates for growth and development some carbohydrates are converted to secondary compounds that can have important functions within the plant.

Secondary Compounds Plant Physiology
Return to Course Map Secondary products or metabolites are compounds produced by plants that appear to have no function in photosynthesis, respiration, solute transport, translocation, protein synthesis, nutrient assimilation, differentiation or the formation of carbohydrates, proteins and most lipids. These compounds have a restricted distribution in the plant kingdom, often being found in only one or a few plant species. However, secondary compounds have important ecological functions in plants. They protect plants against herbivores and pathogens and they serve as attractants for pollinators and seed dispersing animals. Many secondary compounds are toxic to livestock and humans. For more information see “Livestock-Poisoning Plants of California.

Secondary Compounds TERPENES Plant Physiology
Return to Course Map Secondary compounds have been divided into three groups: terpenes, phenolics and nitrogen-containing compounds. Terpenes are the largest class and include diverse substances that are generally insoluble in water. Terpenes defend against herbivores in many ways. Pyrethroids are nonoterpenes, that occur in the leaves and flowers of the Chrysanthemum species, demonstrate insecticidal activity and are the ingredients of some commercial insecticides. Conifers accumulated monoterpenes in resin ducts found in needles, twigs and the trunk. These compounds are toxic to many insects. Some terpenes are associated with odors that repel herbivores and toxins that are poisonous to herbivores. Conifers accumulate monoterpenes

Secondary Compounds PHENOLICS Lignin Flavenoids Tannin
Plant Physiology Secondary Compounds PHENOLICS Return to Course Map Lignin Flavenoids Tannin Phenolic compounds from leaves, roots and decaying litter are sometimes the source of allelopathic compounds that reduce germination and growth of nearby plants. Lignin is a complex phenolic compound found in cell walls of xylem and other conducting plant tissues. While lignin strengthens and protects plants it deters feeding by animals because it is relatively indigestible. Flavenoids are a large class of phenolic compounds that serve to attract animals for pollination and seed dispersal. Some isoflavenoids in legumes have anti-estrogenic effects resulting in infertility of sheep with clover rich diets. Tannins are also phenolic compounds that are common in woody plants. Tannins are general toxins that may significantly reduce growth and survivorship of many herbivores when added to their diets. Cattle and deer commonly avoid plants and plant parts with high tannin contents. Tannins and other phenolics can bind dietary protein in cattle and other animals. Tannins in oak leaves isoflavenoids in legumes

Secondary Compounds Alkaloids Cynanogenic glycosides
Plant Physiology NITROGEN CONTAINING COMPOUNDS Return to Course Map Alkaloids Cynanogenic glycosides Nitrogen-containing compounds include alkaloids and cyanogenic glycosides which are toxic to humans and other animals. Most are biosynthesized from common amino acids. Large numbers of livestock deaths are caused by ingestion of alkaloid-containing plants such as lupines, larkspur and groundsel. Likewise cyanogenic glycosides are widely distributed in the legume and grass families as well as some species in the rose family.

Secondary compounds ALLELOPATHY Plant Physiology
Return to Course Map Some secondary compounds inhibit growth of other plants. Allelopathy is the inhibition of the growth and development of one plant by another. Plants use allelopathy as a means to guard their own space and protect their resources. Allelopathy is a strategy to reduce competition. For example, one way for a tree to protect its root space is to make other trees' roots die off using allelopathy. The tree can then pull more water from the soil for itself.

Plant Physiology Summary Return to Course Map In the plant physiology section you learned about germination and seedling establishment, photosynthesis, carbohydrate storage and allocation, plant water relations and nutrient uptake and secondary compounds. You learned that fire and heat can influence germination along with soil moisture and temperature. You also learned that photosynthetic rate increases with leaf area to some optimum level and then slows with continued increases in leaf area. You learned about three photosynthetic pathways (C3, C4 and CAM) and their adaptive value. You learned that carbohydrates produced during photosynthesis are used for plant growth or stored to meet future needs. And finally you learned about secondary compounds In the plant physiology section you learned about germination and seedling establishment, photosynthesis, carbohydrate storage and allocation, plant water relations and nutrient uptake and secondary compounds. You learned that fire and heat can influence germination along with soil moisture and temperature. You also learned that photosynthetic rate increases with leaf area to some optimum level and then slows with continued increases in leaf area. You learned about three photosynthetic pathways (C3, C4 and CAM) and their adaptive value. You learned that carbohydrates produced during photosynthesis are used for plant growth or stored to meet future needs. And finally you learned about secondary compounds

Photosynthesis Germination and Seedling Establishment Life Cycles and Phenology Secondary Compounds Seasonal Growth Rates You are here Seasonality and Life Cycles Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction Grazing Optimization Now that we have covered Seasonality and Life Cycles, Morphology and Plant Physiology we will now cover that last section entitled “Grazing and Plant Growth.” Range Plant Growth and Development

Grazing and Plant Growth Grazing Effects Grazing Optimization
Grazing Resistance Grazing Effects Grazing and Plant Growth Grazing Resistance Grazing Optimization In this section we will review grazing effects on plant growth, discuss the theory of grazing optimization and finish by investigating plant mechanisms of grazing resistance.

GRAZING & PLANT GROWTH Briske, Chp 4. Dev. Morph and Phys of Grasses. Grazing Resistance Section. Trlica, J Grass Growth and Response to Grazing. A quick lesson in plant structure, growth and regrowth for pasture-based dairy systems. Noy-Meir, I Compensating growth of grazed plants and its relevance to the use of rangelands.

Grazing and Plant Growth
Return to Course Map Grazing Effects Grazing Optimization Grazing Resistance First lets look at grazing effects on plant growth.

Grazing Effects Detrimental Effects Growth Promoting Effects
Grazing and Plant Growth Grazing Effects Return to Course Map Detrimental Effects Growth Promoting Effects Grazing can have detrimental effects and growth promoting effects on plants.

Detrimental Grazing Effects
Grazing and Plant Growth Detrimental Grazing Effects Return to Course Map Removal of photosynthetic tissue Reduced carbohydrate storage Reduced root growth Reduced seed production Some of the detrimental effects include: 1 Removal of photosynthetic tissue, 2 Reduced carbohydrate storage, 3 Reduced root growth and 4. Reduced seed production

Reduced leaf area for photosynthesis
Grazing and Plant Growth Reduced leaf area for photosynthesis Return to Course Map Grazing can influence leaf area Grazing that is too heavy can reduce leaf area. This can reduce photosynthesis. Grazing that is too heavy can reduce leaf area and reduce photosynthesis and carbohydrate production.

Grazing and Plant Growth reduce growth Return to Course Map Return to Course Map Grow leaves, stems, roots and buds. Reduced photosynthesis can result in reduced carbohydrate production. Heavy grazing can weaken root systems increasing moisture stress

Grazing and Plant Growth reduce growth Return to Course Map Thus reduced leaf area can result in less carbohydrates for growth of leaves, stems roots and buds. Leaves, stems, roots and other plant parts Heavy grazing can weaken root systems increasing moisture stress

reduce growth Grazing and Plant Growth Seed production
Return to Course Map Because of its effect on plant productivity grazing may also reduce seed production. Seed production

Reduced carbohydrate storage
Grazing and Plant Growth Reduced carbohydrate storage Return to Course Map Carbohydrates are the plant’s energy source Because reduced leaf area can result in less stored carbohydrates some of the functions that depend on stored carbohydrates may be reduced. In the previous section we discussed the uses of stored carbohydrates Root replacement and growth Regeneration of leaves and stems after dormancy Respiration during dormancy Bud formation Regrowth after top removal by grazing. If stored carbohydrates are reduced then there is less to support these uses.

Grazing Effects Detrimental Effects Growth Promoting Effects
Grazing and Plant Growth Grazing Effects Return to Course Map Detrimental Effects Growth Promoting Effects Grazing sometime has growth promoting effects.

Growth Promoting Effects
Grazing and Plant Growth Growth Promoting Effects Increased photosynthesis Increased tillering Reduced shading Reduced transpiration Return to Course Map Under some circumstances grazing may result in increased photosynthesis. This is a controversial concept that we will discuss more in the section on grazing optimization. Grazing removal of grass top growth may stimulate tillering. Grazing removal of top growth can reduce shading of lower leaves. Because grazing removes leaves it can reduce plant water loss (transpiration) for short periods of time. When these growth promoting effects occur they usually last for only short periods.

Influences on Grazing effects
Grazing and Plant Growth Influences on Grazing effects Return to Course Map Intensity Timing Frequency Grazing of surrounding plants Grazing effects on the productivity of a plant are influenced by the intensity, timing, and frequency of grazing. Competition from neighboring plants can also influence productivity of individual plants. A grazed plant whose neighbors are not grazed may be at a competitive disadvantage. Thus grazing of surround plants can influence the productivity of an individual plant.

Litter Decreases evapotranspiration
Grazing and Plant Growth Litter Return to Course Map Decreases evapotranspiration Moderates surface microclimate during germination and seedling establishment Slows surface runoff and increases infiltration Protects soil from erosion Prolonged heavy grazing reduces the accumulation of litter. Litter acts as a mulch that can reduce ET, moderate surface microclimate during germination and seedling establishment, reduce runoff, improve infiltration and protect the soil from erosion. Accumulation of excessive litter or thatch can suppress seedling establishment of some species giving species that tolerate thatch buildup a competitive advantage. Medusahead is an invasive species that gains a competitive advantage from build up of thatch.

GRAZING TO CLOSE Grazing too close reduces reserves
Grazing and Plant Growth GRAZING TO CLOSE Return to Course Map Grazing too close reduces reserves and slows recovery following grazing Some reports say that grasses can be grazed without damage if 50 to 70 % of the leaf and stem material by weight is left intact as a metabolic reserve to support regrowth. Without this reserve plant productivity and growth can be reduced. One definition of overgrazing is grazing that does not preserve this metabolic reserve. Management that allows prolonged heavy grazing can lead to reduced growth, decrease in plant size and eventual death of grasses and other plants.

Detrimental Effects of Grazing
Grazing and Plant Growth Detrimental Effects of Grazing Return to Course Map Return to Course Map A B C Plant A was allowed to grow for three months without clipping. Healthy root system Plant B was clipped to 3 inches every three weeks for 3 months. Healthy root system Plant C was clipped to 1 inch every week for 3 months. Very weak root system and might not survive a drought These three plants illustrate how management can influence plant productivity. Plant A was allowed to grow for three months without grazing, note the healthy root system. Plant B was clipped to 3 inches every three weeks for three months, it also has a relatively healthy root system. Plant C was clipped to 1 inch every week for 3 months, note the weak root system. Plant B was properly managed. It was not clipped too intensely (closely) and it had a three week regrowth or recovery period between each clipping. Plant C was clipped to closely and too frequently to maintain adequate

Grazing and Plant Growth Summary Return to Course Map Negative effects of heavy grazing vs. possible effects of light to moderate grazing on range plant physiology Heavy Grazing: Decreased photosynthesis Reduced carbohydrate storage Reduced root growth Reduced seed production Reduced ability to compete with ungrazed plants Reduce accumulation of litter or mulch which decreases water infiltration and retention, plus it protects soil from erosion. Light to Moderate Grazing: Increased plant productivity Increased tillering Reduced shading of lower leaves Reduced transpiration losses Reduced ability to compete with ungrazed plants Reduction of excessive litter or mulch that can physically or chemically inhibit vegetative growth. Excessive mulch promotes pathogens and insects that can damage forage plants. In summary, prolonged, heavy grazing can: Decrease photosynthesis Reduce carbohydrate storage Reduce root growth Reduce seed production Reduce the ability to compete with ungrazed plants Reduce accumulation of litter or mulch which increases water infiltration and retention, plus it protects soil from erosion.

Return to Course Map Grazing Effects Grazing Optimization Grazing Resistance Next we will cover the theory of grazing optimization.

There are levels of grazing that can result in increased productivity
Grazing and Plant Growth Grazing Optimization Return to Course Map There are levels of grazing that can result in increased productivity G.O. is a complex and sometime controversial subject. According to the grazing optimization hypothesis there are levels of grazing that can result in increased productivity. However, G.O. is a complex and sometime controversial subject. Grazing was assumed to have a negative effect on primary production until the 1970s when ecologists introduced the grazing optimization hypothesis. This hypothesis states that primary production increases above that of ungrazed vegetation as grazing intensity increases to an optimal level followed by a decrease at greater intensities (McNaughton 1979). Evidence exists to support the occurrence of grazing optimization at both the plant and community levels. However evaluations of research reports in the late 80s and early 90s revealed that only about 20 percent of grazed and ungrazed comparisons resulted in increased primary production. Presumably grazing was too intensive to promote compensatory growth, and this is often the case in commercial grazing systems. The grazing pattern required to increase primary production is often an intensive early season grazing followed by a long period of little or no grazing. Consequently, an absolute increase in plant growth is rarely documented in grazing ecosystems because plants do not have a sufficient opportunity for recovery following defoliation, and primary production generally decreases with increasing grazing severity compared to that of ungrazed communities.

Grazing Optimization HYPOTHESIS
Grazing and Plant Growth Grazing Optimization HYPOTHESIS Return to Course Map The grazing optimization hypothesis proposes three potential responses of primary production to increasing grazing intensity. Primary production may decrease with increasing intensity as in line A on this graph, it can remain unaffected until intermediate levels of grazing intensity are reached and then decrease as in B or productivity can increase with increasing grazing intensity to an optimal level and then decrease at greater grazing intensities The term over-compensation has been used for this increase to an optimal level while the term undercompensation has been used to define responses A and B.

Grazing Optimization HYPOTHESIS
Grazing and Plant Growth Grazing Optimization HYPOTHESIS Return to Course Map NPP=GPP - R GPP and NPP increase as leaves are added until upper leaves begin shading lower leaves then R increases resulting in decrease in NPP The NPP=GPP – R formula can be used to explain one way for plant productivity to increase under grazing. In the photosynthesis section this slide shows that production resulting from photosynthesis is expressed as gross primary production (GPP) and net primary production (NPP). NPP is GPP minus respiration (R). Following clipping or grazing GPP and NPP initially increase as leaf area increases but as upper leaves

Grazing Optimization Grazing and Plant Growth NPP=GPP - R
Return to Course Map NPP=GPP - R GPP and NPP increase as leaves are added until upper leaves begin shading lower leaves then R increases resulting in decrease in NPP Grazing reduces leaf area G.O. says if grazing keeps LAI near 4, NPP is optimized. May occur in some species, more likely in pasture. Some species are extremely susceptible to grazing even at light intensities. If you could graze to maintain leaf area at around 4 you could maximize NPP. That should keep the plant productive. On pasture and alfalfa fields that have a long growing season it is possible to manipulate leaf area through grazing control and mowing height and frequency. Thus grazing or mowing can be used to improve forage production. On rangeland the growing season is usually so short that plants move on in life cycle to flowering and seed production that has greater influence on physiology than grazing. You will hear of grazing optimization which is the idea that grazing can increase plant productivity. This is the basis for that idea and it has been demonstrated on pasture and some grasslands.

Grazing Optimization Grazing and Plant Growth
Return to Course Map C = ‘control’ no clipping TB = terminal bud removed only 60 = 60% current annual growth removed 100 = 100% current annual growth removed Sagebrush (Artemisia tridentata) and bitterbrush (Purshia tridentata) are two common shrubs in the Great Basin. When researchers compared three clipping treatments (no clipping, terminal bud removal, removal of 60 % of current growth and removal of 100 % of current growth) they found that Artemisia growth was reduced relative to the no clipping treatment and Purshia growth increased relative to the no clipping treatment. This suggests that Artemisia undercompensates after browsing and Purshia overcompensates following browsing. This study found that Artemisia was unable to maintain high vigor under heavy browsing but was better able to withstand drought while Purshia maintained high vigor under browsing but was sensitive to drought. They concluded that increased aboveground biomass production in browsed Purshia may have been at the expense of root growth (Bilbrough and Richards 1993). Sagebrush, Artemisia tridentata and bitterbrush (Purshia tridentata) are two common shrubs in the Great Basin. In a comparison of Artemisia and Purshia researchers found that Purshia compensated for the loss of tissue to a greater extent than Artemisia. In comparison to unclipped branches, Artemisia and Purshia both increased the frequency of new long shoots produced in response to simulated browsing. However, Artemisia tended toward reduced long shoot biomass with increased browsing, while Purshia was either insensitive to the severity of browsing treatment or, in one case, increased long shoot biomass after treatment. The contrasting responses were particularly evident in the most severe treatment, which resulted in death of all Artemisia branches but in biomass production equal to controls in Purshia. Additionally, node production declined in Artemisia but in Purshia was equal to or exceeded node production in control unclipped branches. In this study, neither aboveground resource availability nor bud availability fully explained differences in the abilities of Artemisia and Purshia to tolerate browsing. In addition, the results from this and related studies suggest that inherent relative growth rate was not correlated with herbivory tolerance in these species. Developmental plasticity and the resultant altered resource allocation patterns following winter browsing appear to distinguish Artemisia and Purshia in their ability to tolerate browsing. Key words: Artemisia tridentata;b rowsing tolerance;

Grazing Optimization Grazing and Plant Growth
Return to Course Map A study in Yellowstone National Park found that aboveground productivity of grazed vegetation was 47% higher than that of ungrazed vegetation. One explanation for this increased production is overcompensation following grazing (Frank and McNaughton 1993). across sites (P < ). This result could be explained by either a methodological or grazer effect. We believe it was the latter. Results from a computer simulation showed that sequential sampling with temporary exclosures resulted in a slight underestimation of production, suggesting that the reported differences between treatments were conservative. We suggest that stimulation of aboveground production by ungulates may be, in part, due to the migratory behavior of native ungulates that track young, high quality forage as it shifts spatially across the Yellowstone ecosystem. These three plants illustrate how management can influence plant productivity.

Mechanisms contributing to compensatory plant growth
Grazing and Plant Growth Herbivore-induced physiological processes Accelerated photosynthesis per unit leaf area Accelerated nutrient absorption per unit root mass Greater resource allocation to shoots Increased tiller initiation Improved water status Herbivore-mediated environmental modification Increased irradiance on remaining leaves and young tillers Conservation of soil water following leaf area removal Accelerated rate of nutrient cycling Increased activity of decomposer organisms Return to Course Map There are several mechanisms that can contribute to compensatory growth or over-compensation. Some are the direct result of herbivory including Accelerated photosynthesis per unit leaf area Accelerated nutrient absorption per unit root mass Greater resource allocation to shoots Increased tiller initiation Improved water status Others are the result of environmental modifications that are mediated by herbivory including: Increased irradiance on remaining leaves and young tillers Conservation of soil water following leaf area removal Accelerated rate of nutrient cycling Increased activity of decomposer organisms

Mechanisms contributing to compensatory plant growth
Grazing and Plant Growth Grazing and Plant Growth Grazing Effects Grazing Optimization Grazing Resistance Return to Course Map In this final section we will look at two general ways that plants resist or survive the effects of grazing.

Grazing Resistance Grazing and Plant Growth
Return to Course Map Grazing resistance can be divided into avoidance and tolerance. Avoidance mechanisms decrease the probability of being grazed. Tolerance allows the plant to increase growth following grazing.

Grazing avoidance Mechanical Biochemical Grazing and Plant Growth
Return to Course Map Mechanical Biochemical Tissue accessibility is a form of mechanical avoidance of grazing and is primarily dependent on the degree of elevation of leaves and tillers above the soil surface. Another form of avoidance is formation of spines, abrasive awns or epidermal characteristics like pubescence or cuticular wax that make plants unpalatable or unpleasant to touch. Biochemical avoidance comes in the form of secondary compounds that reduce palatability or are toxic such as alkaloids, tannins and cyanogenic glycosides.

Grazing tOLERANCE Plant Morphology
Grazing and Plant Growth Grazing tOLERANCE Return to Course Map Plant Morphology Grass, forb and shrub species produce viable axillary buds have greater potential to regrow following grazing Grass, forb, and shrub species that protect meristems have the potential to regrow quickly following grazing. Grasses that develop tillers at different times during the grazing season tolerate grazing better than plants that do not Morphological mechanisms that increase growth following grazing are one means that plants have to tolerate grazing. For example: Grass, forb, and shrub species that produce and maintain many viable axillary buds tolerate grazing because they have the potential to regrow following grazing. Grass, forb, and shrub species that protect meristems (growing points) have the potential to regrow quickly following grazing, thus reducing the amount of nutrients and water needed to regrow. Some grasses and forbs do not elevate apical meristems until late in the growing season, thereby protecting meristems from grazing. Grasses that develop tillers at different times during the grazing season tolerate grazing better than plants that do not, because not all tillers can be grazed at the same time.

Grazing tOLERANCE PLANT PHYSIOLOGY
Grazing and Plant Growth Grazing tOLERANCE Return to Course Map PLANT PHYSIOLOGY Ability to regrow quickly following grazing Ability to compete for water and nutrients enable some plants to regrow more quickly In some plant grazing stimulates absorption of nutrients. However, in many species removal of leaves and stems decreases nutrient absorption. Ability to quickly move nutrients and carbohydrates between roots and shoots Physiological mechanisms that increase growth following grazing are another means that plants have to tolerate grazing. For example: The ability to regrow quickly following grazing is important because it enables plants to quickly reestablish leaf tissue that creates energy through photosynthesis. Plants that regrow quickly often have increased photosynthetic rates in regrowth and remaining foliage. 2. A superior ability to compete for resources - water and nutrients - needed to quickly regrow enables some plants to tolerate grazing better than others. 3. In some plants, grazing stimulates absorption of nutrients like phosphorus, which enables those species to tolerate grazing better than others. However, in many species, removal of leaves and stems decreases nutrient absorption because of a decrease in the root surface area. 4. Plants that quickly move resources among shoots or from roots to shoots tolerate grazing better than plants that do not. This enables rapid adjustment of carbon and nutrient distribution among plant parts, which enhances competitive ability and survival. Ref:BEHAVE - carbohydrates

Grazing RESISTANCE FACTORS
Grazing and Plant Growth Grazing RESISTANCE FACTORS Return to Course Map Grasses Higher proportion of culmless (stemless) shoots than species with low resistance Greater delay in elongation of the apical buds than species with low resistance Sprout more freely from basal buds after defoliation than species with low resistance. Higher ratio of vegetative to reproductive stems than species with low resistance. Grass characteristics that resist the effects of grazing include (read the list)

Grazing and Plant Growth Grazing RESISTANCE FACTORS Return to Course Map Forbs Produce a large number of viable seeds Delayed elevation of growing points Poisons and chemical compounds that reduce palatability Forbs resist grazing by (read the list)

Grazing and Plant Growth Grazing RESISTANCE FACTORS Return to Course Map Shrubs Spines and thorns volatile oils and tannins that reduce palatability Branches make removal of inner leaves difficult Only current year’s growth is palatable and nutritious for most species.

GRAZING RESISTANCE OF FORAGE
Grazing and Plant Growth GRAZING RESISTANCE OF FORAGE Return to Course Map Most to least resistant Grasses Shrubs Forbs *Many exceptions do occur. Generally grasses are considered most resistant to grazing followed by shrubs and finally forbs.

Grazing and Plant Growth Summary Return to Course Map In the final section you learned about grazing and plant responses to grazing. You learned that grazing can have detrimental as well as growth promoting effects on plants. We discussed the theory of grazing optimization and some of the mechanisms that can result in compensatory plant growth. And finally we discussed mechanisms that allow plants to resist the effects of grazing. In the final section you learned about grazing and plant responses to grazing. You learned that grazing can have detrimental as well as growth promoting effects on plants. We discussed the theory of grazing optimization and some of the mechanisms that can result in compensatory plant growth. An finally we discussed mechanisms that allow plants to resist the effects of grazing.

The end: unused slides

Seasonality and Life Cycles Reading and references SEASONALITY & LIFE CYCLES Return to Course Map The Phenology Handbook, pg 1-15 George et al Annual Range Forage Production George and Bell Using Stage of Maturity……..

MORPHOLOGY Briske, Chp 4. Dev. Morph and Phys of Grasses. Introduction and Developmental Morphology Sections. Skinner and Moore. Growth and Dev of Forage Plants How Grass Grows

Plant physiology McKell, C.M Morphogenesis and management of annual range plants in the United States. Pg Briske, Chp 4. Dev. Morph and Phys of Grasses. Grazing Resistance Section. Waller and Lewis Occurrence of C3 and C4 photosynthetic pathways in North American grasses. Carbohydrate Reserves: What you learned may be wrong. Reading references for the Plant Physiology Section are provide on this slide with links to the references.

GRAZING & PLANT GROWTH Briske, Chp 4. Dev. Morph and Phys of Grasses. Grazing Resistance Section. Trlica, J Grass Growth and Response to Grazing. A quick lesson in plant structure, growth and regrowth for pasture-based dairy systems. Noy-Meir, I Compensating growth of grazed plants and its relevance to the use of rangelands.

Plant physiology McKell, C.M Morphogenesis and management of annual range plants in the United States. Pg Briske, Chp 4. Dev. Morph and Phys of Grasses. Grazing Resistance Section. Waller and Lewis Occurrence of C3 and C4 photosynthetic pathways in North American grasses. Carbohydrate Reserves: What you learned may be wrong. Reading references for the Grazing and Plant Growth Section are provide on this slide with links to the references.

Grass Anatomy Forb Anatomy Reproduction
Morphology Grass Anatomy Growing Points (buds, meristems) Developmental Anatomy Forb Anatomy Reproduction Sexual Asexual Return to Course Map In this section we will discuss the morphology and development of grasses and forbs and plant reproduction.

Plant physiology Plant Physiology
Return to Course Map Germination and Seedling Establishment Photosynthesis Factors that influence photosysnthesis C3, C4, CAM Photosynthesis Carbohydrates and Carbohydrate Allocation Water and Nutrients Secondary Compounds Let’s begin the plant physiology section with an overview of germination and seedling establishment.

Return to Course Map Grazing and Plant Growth Grazing Effects Grazing Optimization Grazing Resistance

Physiology and Morphology of Range Plants
Photosynthesis Germination and seeding establishment Life Cycles And Phenology Secondary Compounds Seasonal Growth Rates Seasonality and Life Cycle Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Carb. Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction You are here Grazing Optimization Now that we have covered the seasonality of range plant growth we will move on to plant morphology. Physiology and Morphology of Range Plants 150

Photosynthesis Germination and seeding establishment Life Cycles And Phenology Secondary Compounds Seasonal Growth Rates Seasonality and Life Cycle Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Carb. Allocation RDM You are here Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction Grazing Optimization Physiology and Morphology of Range Plants 151

Photosynthesis Germination and seeding establishment Life Cycles And Phenology Secondary Compounds Seasonal Growth Rates Seasonality and Life Cycle Plant Physiology Forage Quality Water and Nutrients Carbohydrates and Carb. Allocation RDM Grass Anatomy Forb Anatomy Grazing Effects Grazing and Plant Growth Morphology Shrub Anatomy Grazing Resistance Reproduction You are here Grazing Optimization Physiology and Morphology of Range Plants 152

Chapter 5: Range Plant Physiology
1. Basic concepts of plant growth 2. Importance of carbohydrate reserves 3. Grazing effect on forage plants 4. Grazing resistance in grasses, forbs and shrubs 5. Grazing theory a. Why palatable plants dominate rangelands with good grazing management? b. Why unpalatable plants dominate rangelands under sustained heavy grazing (over grazing)?

A few basic principles concerning the influence of grazing on plants
1. Plants must have leaves for photosynthesis. 2. Grazing has the least effect on plants during the dormant season when they are photosynthetically inactive. 3. Grazing has the most severe effect on plants towards the end of the growing season ( seed formation to seed hardening) because the plant’s demands for carbohydrates are higher and little time remains of optimal temperature and moisture conditions for regrowth. 4. Grazing early in the growing season has less effect on plants than late in the growing season because considerable time remains when temperature and moisture are optimal for regrowth.

Why plants must store carbohydrates
1. Root replacement and growth 2. Regeneration of leaves and stems after dormancy 3. Respiration during dormancy 4. Bud formation 5. Regrowth after top removal by grazing.

Photosynthesis and Carbohydrates
Factors that influence photosysnthesis C3, C4, CAM Photosynthesis Carbohydrates and Carbohydrate Allocation

Reproduction Recruitment maintains plant community
Sexual Reproduction (flowers and seeds) Vegetative Reproduction (stolons, rhizomes) Annuals dependent on seed production Short-lived perennials depend on seed production Long-lived perennials rely more on vegetative reproduction.

Relationship between herbage dry matter and leaf area (Brougham 1956)

Increased photosynthesis

Increased tillering Increased photosynthesis Reduced transpiration

Reduced shading

Reduced transpiration

Summary Effects of Light to Moderate Grazing
Increased plant productivity Increased tillering Reduced shading of lower leaves Reduced transpiration losses Reduced ability to compete with ungrazed plants Reduction of excessive litter or mulch that can physically or chemically inhibit vegetative growth. Excessive mulch promotes pathogens and insects that can damage forage plants. Light to Moderate Grazing 165

Plants use inorganic minerals for nutrition
Plants use inorganic minerals for nutrition. Complex interactions involving decomposition of rocks, organic matter, animals and microbes take place to form inorganic nutrient ions in soil water. Roots absorb these mineral ions if they are readily available. They can be tied up by other elements or by alkaline or acidic soils. Soil microbes also assist in ion uptake.

Mycorrhizae are a mutualism between plants and fungi
Mycorrhizae are a mutualism between plants and fungi. The plant provides the fungus with carbohydrates and the fungus helps the plant get nutrients from the soil, like nitrogen. Plants make carbohydrates from carbon dioxide and sunlight and their growth is usually limited by nitrogen. While fungi can absorb nitrogen and phosphorus from the soil, they can’t make their own carbohydrates.

Life cycles Return to Course Map Plants must be adapted to seasonal changes in solar intensity, temperature, water availability, and day length. Many plants survive cold winters in a dormant state while others tolerate cold temperatures. These plants respond to warming temperatures and available moisture by initiating growth and proceeding through the growing season until cooling temperatures, day length or drying soil signal the beginning of dormancy. Some plants, must survive a dry season in a dormant state. These plants start to grow with the beginning of the rainy season proceeding through the growing season until drying soil signals the beginning of the dry season dormancy. Native perennial grasses and forbs in California’s foothill rangelands commonly enter a dormant or near dormant state during the dry season. Image courtesy of

Bilbrough and Richards (1993)
Grazing and Plant Growth Bilbrough and Richards (1993) Return to Course Map Sagebrush (Artemisia tridentata) and bitterbrush (Purshia tridentata) are two common shrubs in the Great Basin. When researchers compared three clipping treatments (no clipping, terminal bud removal, removal of 60 % of current growth and removal of 100 % of current growth) they found that Artemisia growth was reduced relative to no clipping treatment and Purshia growth increased relative to the no clipping treatment. This suggests that Artemisia undercompensates after browsing and Purshia overcompensates following browsing. There research found that Artemisia was unable to maintain high vigor under heavy browsing but was better able to withstand drought while Purshia maintained high vigor under browsing but was sensitive to drought. They concluded that increased aboveground biomass production in browsed Purshia may have been at the expense of root growth Bilbrough and Richards (1993) Sagebrush, Artemisia tridentata and bitterbrush (Purshia tridentata) are two common shrubs in the Great Basin. In a comparison of Artemisia and Purshia researchers found that Purshia compensated for the loss of tissue to a greater extent than Artemisia. In comparison to unclipped branches, Artemisia and Purshia both increased the frequency of new long shoots produced in response to simulated browsing. However, Artemisia tended toward reduced long shoot biomass with increased browsing, while Purshia was either insensitive to the severity of browsing treatment or, in one case, increased long shoot biomass after treatment. The contrasting responses were particularly evident in the most severe treatment, which resulted in death of all Artemisia branches but in biomass production equal to controls in Purshia. Additionally, node production declined in Artemisia but in Purshia was equal to or exceeded node production in control unclipped branches. In this study, neither aboveground resource availability nor bud availability fully explained differences in the abilities of Artemisia and Purshia to tolerate browsing. In addition, the results from this and related studies suggest that inherent relative growth rate was not correlated with herbivory tolerance in these species. Developmental plasticity and the resultant altered resource allocation patterns following winter browsing appear to distinguish Artemisia and Purshia in their ability to tolerate browsing. Key words: Artemisia tridentata;b rowsingt olerance; C = ‘control’ no clipping TB = terminal bud removed only 60 = 60% current annual growth removed 100 = 100% current annual growth removed

Return to Course Map A study in Yellowstone National Park found that aboveground productivity of grazed vegetation was 47% higher than that of ungrazed vegetation. One explanation for increased production is overcompensation following grazing (Frank and McNaughton 1993). across sites (P < ). This result could be explained by either a methodological or grazer effect. We believe it was the latter. Results from a computer simulation showed that sequential sampling with temporary exclosures resulted in a slight underestimation of production, suggesting that the reported differences between treatments were conservative. We suggest that stimulation of aboveground production by ungulates may be, in part, due to the migratory behavior of native ungulates that track young, high quality forage as it shifts spatially across the Yellowstone ecosystem.These three plants illustrate how management can influence plant productivity.

Carbohydrate storage Root replacement and growth
Grazing and Plant Growth Carbohydrate storage Return to Course Map Root replacement and growth Regeneration of leaves and stems after dormancy Respiration during dormancy Bud formation Regrowth after top removal by grazing. In the previous section we discussed the uses of stored carbohydrates Root replacement and growth Regeneration of leaves and stems after dormancy Respiration during dormancy Bud formation Regrowth after top removal by grazing. We can probably delete this slide

GRAZING OPTIMIZATION Grazing and Plant Growth
Return to Course Map Can probably delete this slide Grazing was assumed to have a negative effect on primary production until the 1970s when ecologists introduced the grazing optimization hypothesis. This hypothesis states that primary production increases above that of ungrazed vegetation as grazing intensity increases to an optimal level followed by a decrease at greater intensities (McNaughton 1979). Evidence exists to support the occurrence of grazing optimization at both the plant and community levels. However evaluations of research reports in the late 80s and early 90s revealed that only about 20 percent of grazed and ungrazed comparisons resulted in increased primary production. Presumably grazing was too intensive to promote compensatory growth, and this is often the case in commercial grazing systems. The grazing pattern required to increase primary production is often an intensive early season grazing followed by a long period of little or no grazing. Consequently, an absolute increase in plant growth is rarely documented in grazing ecosystems because plants do not have a sufficient opportunity for recovery following defoliation, and primary production generally decreases with increasing grazing severity compared to that of ungrazed communities. 178

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