FACTORS AFFECTING PLANT GROWTH

MEASURING GROWTH Increase in fresh weight Increase in dry weight Volume Length Height Surface area

HOW PLANTS GROW Meristems Dicots Apical meristems – vegetative buds shoot tips axils of leaves Cells divide/redivide by mitosis/cytokinesis Cell division/elongation causes shoot growth Similar meristematic cells at root tips

HOW PLANTS GROW Meristems (cont) Secondary growth in woody perennials Increase in diameter due to meristematic regions vascular cambium xylem to inside, phloem to outside cork cambium external to vascular cambium produces cork in the bark layer

Plant Growth and Development Photosynthesis Respiration Transpiration The above 3 items drive plant growth

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light Temperature Water Humidity Gases Nutrition It is important to know how these factors affect plant growth and development. With a basic understanding of these factors, you may be able manipulate plants to meet your needs. By recognizing the role of these factors, you may be better able to diagnose problems caused by environmental stress.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light Sun’s radiation not all reaches earth; atmosphere absorbs much visible (and some invisible) rays pass, warming surface reradiation warms atmosphere Intensity high in deserts; no clouds, dry air low in cloudy, humid regions earth tilted on axis; rays strike more directly in summer day length varies during year due to tilt

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH PAR (Photosynthetically Active Radiation) Plants absorb blue and red light. Blue light is mainly responsible for vegetative growth. Red light when combined with blue light encourages flowering.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Light (cont) Photoperiodism – response to varying length of light and dark It was first believed that day length was the main factor affecting plant flowering. However, it was later found out that it was the length of darkness.

Plants are classified into 3 day length categories: Short day length plants flower when they are exposed to less than 12 hr. sunlight (mums, X-mas cactus, poinsettias) Long day plants flower when the day length exceeds 12 hours. This includes most summer flowering plants and vegetables. Day neutral plants flower regardless of day length such as tomatoes, corn, cucumber, and strawberry. Duration - Photoperiodism - Plant behavior in relation to day length - long day plants - flower only if days are longer than same critical period - 12 hours Grains and clovers - short day plants - flower only if days are shorter than a critical period soybeans. - indeterminate - flower over a wide range of day lengths. Tomato, cotton, buckwheat Some crops fail to flower in certain geographical areas Chrysanthemums can be made to bloom by controlling photoperiod.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Temperature high light intensity creates heat; sunburned low temp injury associated with frosts Low temperatures reduce energy use and increase sugar storage. Citrus is sweeter after cold weather. Adverse temp. may cause stunted growth and poor quality. High temperatures cause bitter lettuce.

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Water most growing plants contain about 90% water amount needed for growth varies with plant and light intensity transpiration drives water uptake from soil water pulled through xylem exits via stomates evapotranspiration - total loss of water from soil loss from soil evaporation and plant transpiration

ENVIRONMENTAL FACTORS INFLUENCING PLANT GROWTH Gases Nitrogen is most abundant Oxygen and carbon dioxide are most important plants use CO2 for photosynthesis; give off O2 plants use O2 for respiration; give off CO2 stomatal opening and closing related to CO2 levels oxygen for respiration limited in waterlogged soils increased CO2 levels in atmosphere associated with global warming additional pollutants harm plants