1. Chapter 37
Plant Nutrition

2. Overview: A Nutritional Network Every organism
Continually exchanges energy and materials with its environment
For a typical plant
Water and minerals come from the soil, while carbon dioxide comes from the air

3. The branching root system and shoot system of a vascular plant
Ensure extensive networking with both reservoirs of inorganic nutrients
Figure 37.1

4. Plants derive most of their organic mass from the CO2 of air
Concept 37.1: Plants require certain chemical elements to complete their life cycle
Plants derive most of their organic mass from the CO2 of air
But they also depend on soil nutrients such as water and minerals
Figure 37.2
CO2, the source
of carbon for
Photosynthesis,
diffuses into
leaves from the
air through
stomata.
Through
stomata, leaves
expel H2O and
O2.
H2O O2
CO2
Roots take in
O2 and expel
CO2. The plant
uses O2 for cellular
respiration but is a net O2 producer.
Roots absorb
H2O and
minerals from
the soil.
Minerals

5. Macronutrients and Micronutrients
More than 50 chemical elements
Have been identified among the inorganic substances in plants, but not all of these are essential
A chemical element is considered essential
If it is required for a plant to complete a life cycle

6. Researchers use hydroponic culture
To determine which chemicals elements are essential
Figure 37.3
TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential.
RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral deficiencies in soil.
Control: Solution
containing all minerals
Experimental: Solution
without potassium
APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants.

7. Essential elements in plants
Table 37.1

8. Nine of the essential elements are called macronutrients
Because plants require them in relatively large amounts
The remaining eight essential elements are known as micronutrients
Because plants need them in very small amounts

9. Symptoms of Mineral Deficiency
The symptoms of mineral deficiency
Depend partly on the nutrient’s function
Depend on the mobility of a nutrient within the plant

10. Deficiency of a mobile nutrient
Usually affects older organs more than young ones
Deficiency of a less mobile nutrient
Usually affects younger organs more than older ones

11. The most common deficiencies
Are those of nitrogen, potassium, and phosphorus
Figure 37.4
Phosphate-deficient
Healthy
Potassium-deficient
Nitrogen-deficient

12. Concept 37.2: Soil quality is a major determinant of plant distribution and growth
Along with climate
The major factors determining whether particular plants can grow well in a certain location are the texture and composition of the soil
Texture
Is the soil’s general structure
Composition
Refers to the soil’s organic and inorganic chemical components

13. Texture and Composition of Soils
Various sizes of particles derived from the breakdown of rock are found in soil
Along with organic material (humus) in various stages of decomposition
The eventual result of this activity is topsoil
A mixture of particles of rock and organic material

14. The topsoil and other distinct soil layers, or horizons
Are often visible in vertical profile where there is a road cut or deep hole
Figure 37.5
The A horizon is the topsoil, a mixture of
broken-down rock of various textures, living
organisms, and decaying organic matter.
The B horizon contains much less organic
matter than the A horizon and is less
weathered.
The C horizon, composed mainly of partially
broken-down rock, serves as the “parent”
material for the upper layers of soil. A B C

15. The film of loosely bound water
After a heavy rainfall, water drains away from the larger spaces of soil
But smaller spaces retain water because of its attraction to surfaces of clay and other particles
The film of loosely bound water
Is usually available to plants
Figure 37.6a
(a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root.
Soil particle surrounded by
film of water
Root hair
Water available to plant
Air space

16. Acids derived from roots contribute to a plant’s uptake of minerals
When H+ displaces mineral cations from clay particles
Figure 37.6b
(b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by secreting it from root hairs and also by cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil solution.
H2O + CO2
H2CO3
HCO3– +
Root hair K+
Cu2+
Ca2+
Mg2+ H+
Soil particle –

17. Soil Conservation and Sustainable Agriculture
In contrast to natural ecosystems
Agriculture depletes the mineral content of the soil, taxes water reserves, and encourages erosion
The goal of soil conservation strategies
Is to minimize this damage

18. Commercially produced fertilizers
Contain minerals that are either mined or prepared by industrial processes
“Organic” fertilizers
Are composed of manure, fishmeal, or compost

19. Agricultural researchers
Are developing ways to maintain crop yields while reducing fertilizer use
Genetically engineered “smart” plants
Inform the grower when a nutrient deficiency is imminent
Figure 37.7
No phosphorus deficiency
Beginning phosphorus
deficiency
Well-developed phosphorus

20. Irrigation
Irrigation, which is a huge drain on water resources when used for farming in arid regions
Can change the chemical makeup of soil

21. Topsoil from thousands of acres of farmland
Erosion
Topsoil from thousands of acres of farmland
Is lost to water and wind erosion each year in the United States

22. Certain precautions
Can prevent the loss of topsoil
Figure 37.8

23. The goal of soil management
Is sustainable agriculture, a commitment embracing a variety of farming methods that are conservation-minded

24. Some areas are unfit for agriculture
Soil Reclamation
Some areas are unfit for agriculture
Because of contamination of soil or groundwater with toxic pollutants
A new method known as phytoremediation
Is a biological, nondestructive technology that seeks to reclaim contaminated areas

25. Plants require nitrogen as a component of
Concept 37.3: Nitrogen is often the mineral that has the greatest effect on plant growth
Plants require nitrogen as a component of
Proteins, nucleic acids, chlorophyll, and other important organic molecules

26. Soil Bacteria and Nitrogen Availability
Nitrogen-fixing bacteria convert atmospheric N2
To nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis
Figure 37.9
Atmosphere N2
Soil
Nitrogen-fixing bacteria
Organic material (humus)
NH3 (ammonia)
NH4+ (ammonium)
H+ (From soil)
NO3– (nitrate)
Nitrifying bacteria
Denitrifying bacteria
Root
NH4+
Nitrate and nitrogenous organic compounds exported in xylem to shoot system
Ammonifying bacteria

27. Improving the Protein Yield of Crops
Agriculture research in plant breeding
Has resulted in new varieties of maize, wheat, and rice that are enriched in protein
Such research
Addresses the most widespread form of human malnutrition: protein deficiency

28. Concept 37.4: Plant nutritional adaptations often involve relationships with other organisms
Two types of relationships plants have with other organisms are mutualistic
Symbiotic nitrogen fixation
Mycorrhizae

29. The Role of Bacteria in Symbiotic Nitrogen Fixation
Symbiotic relationships with nitrogen-fixing bacteria
Provide some plant species with a built-in source of fixed nitrogen
From an agricultural standpoint
The most important and efficient symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

30. Along a legumes possessive roots are swellings called nodules
Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria
Figure 37.10a
(a) Pea plant root. The bumps on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant.
Nodules
Roots

31. Inside the nodule
Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell
5 m
Bacteroids
within
vesicle
(b) Bacteroids in a soybean root nodule. In this TEM, a cell from a root nodule of soybean is filled with bacteroids in vesicles. The cells on the left are uninfected.
Figure 37.10b

32. The bacteria of a nodule
Obtain sugar from the plant and supply the plant with fixed nitrogen
Each legume
Is associated with a particular strain of Rhizobium

33. Development of a soybean root nodule
Infection thread
Rhizobium bacteria
Dividing cells in root cortex
Bacteroid
2 The bacteria penetrate the cortex within the Infection thread. Cells of the cortex and pericycle begin dividing, and vesicles containing the bacteria bud into cortical cells from the branching infection thread. This process results in the formation of bacteroids.
Developing root nodule
Dividing cells in pericycle
Infected root hair 1 2 3
Nodule vascular tissue 4
3 Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse, forming the nodule.
Roots emit chemical signals that attract Rhizobium bacteria. The bacteria then emit signals that stimulate root hairs to elongate and to form an infection thread by an invagination of the plasma membrane. 1
The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant.
Figure 37.11

34. The Molecular Biology of Root Nodule Formation
The development of a nitrogen-fixing root nodule
Depends on chemical dialogue between Rhizobium bacteria and root cells of their specific plant hosts

35. Symbiotic Nitrogen Fixation and Agriculture
The agriculture benefits of symbiotic nitrogen fixation
Underlie crop rotation
In this practice
A non-legume such as maize is planted one year, and the following year a legume is planted to restore the concentration of nitrogen in the soil

36. Mycorrhizae and Plant Nutrition
Are modified roots consisting of mutualistic associations of fungi and roots
The fungus
Benefits from a steady supply of sugar donated by the host plant
In return, the fungus
Increases the surface area of water uptake and mineral absorption and supplies water and minerals to the host plant

37. The Two Main Types of Mycorrhizae
In ectomycorrhizae
The mycelium of the fungus forms a dense sheath over the surface of the root
a Ectomycorrhizae. The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate. Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant.
Mantle (fungal sheath)
Epidermis
Cortex
Endodermis
Fungal hyphae between cortical cells
(colorized SEM)
100 m
(a)
Figure 37.12a

38. In endomycorrhizae Microscopic fungal hyphae extend into the root
Figure 37.12b
Epidermis
Cortex
Fungal hyphae
Root hair
10 m
(LM, stained specimen)
Cortical cells
Endodermis
Vesicle
Casparian strip
Arbuscules
2 Endomycorrhizae. No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex.
(b)

39. Agricultural Importance of Mycorrhizae
Farmers and foresters
Often inoculate seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae

40. Epiphytes, Parasitic Plants, and Carnivorous Plants
Some plants
Have nutritional adaptations that use other organisms in nonmutualistic ways

41. Staghorn fern, an epiphyte Mistletoe, a photosynthetic parasite
Exploring unusual nutritional adaptations in plants
Staghorn fern, an epiphyte
EPIPHYTES
PARASITIC PLANTS
CARNIVOROUS PLANTS
Mistletoe, a photosynthetic parasite
Dodder, a nonphotosynthetic parasite
Host’s phloem
Haustoria
Indian pipe, a nonphotosynthetic parasite
Venus’ flytrap
Pitcher plants
Sundews
Dodder
Figure 37.13