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
The root and shoot systems of a vascular plant ensure extensive networking with both reservoirs of inorganic nutrients

4. 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

5. LE 37-2
CO2
H2O O2 O2
Minerals
CO2
H2O

6. Macronutrients and Micronutrients
More than 50 chemical elements have been identified among the inorganic substances in plants, but not all of these are essential to plants
A chemical element is considered essential if it is required for a plant to complete its life cycle
Researchers use hydroponic culture to determine which chemicals elements are essential

7. LE 37-3
Control: Solution
containing all minerals
Experimental: Solution
without potassium

9. Nine of the essential elements are called macronutrients because plants require them in relatively large amounts
The remaining eight are called micronutrients because plants need them in very small amounts

10. Symptoms of Mineral Deficiency
Symptoms of mineral deficiency depend on the nutrient’s function and mobility within the plant
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
The most common deficiencies are those of nitrogen, potassium, and phosphorus

11. Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient
LE 37-4
Healthy
Phosphate-deficient
Potassium-deficient
Nitrogen-deficient

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

13. Texture and Composition of Soils
Topsoil is a mixture of particles of rock, living organisms, and humus (the remains of partially decayed organic material)
The topsoil and other distinct soil layers, or horizons, are often visible in vertical profile where there is a road cut or deep hole

14. LE 37-5 A B C

15. Animation: How Plants Obtain Minerals from Soil
After a heavy rainfall, water drains from the larger spaces of soil, but smaller spaces retain water because of its attraction to clay and other particles
The film of loosely bound water is usually available to plants
Animation: How Plants Obtain Minerals from Soil

16. LE 37-6 Soil particle surrounded by film of water Soil particle
Root hair
Water
available
to plant
Root hair
Air space
Soil water
Cation exchange in soil

17. Acids derived from roots contribute to a plant’s uptake of minerals when H+ displaces mineral cations from clay particles

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

19. Fertilizers
Commercial fertilizers contain minerals that are mined or prepared by industrial processes
Organic fertilizers are composed of manure, fishmeal, or compost

20. 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

21. No phosphorus deficiency Beginning phosphorus deficiency
LE 37-7
No phosphorus
deficiency
Beginning
phosphorus
deficiency
Well-developed
phosphorus
deficiency

22. Irrigation
Irrigation is a huge drain on water resources when used for farming in arid regions
It can change the chemical makeup of soil

23. Erosion
Topsoil from thousands of acres of farmland is lost to water and wind erosion each year in the United States
Precautions, such as contour tillage, can prevent loss of topsoil

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

26. Soil Reclamation
Some areas are unfit for agriculture because of contamination of soil or groundwater with toxic pollutants
Phytoremediation is a biological, nondestructive technology that reclaims contaminated areas

27. 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

28. 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

29. 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

30. 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, involving roots and bacteria
Mycorrhizae, involving roots and fungi

31. 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
For agriculture, the key symbioses between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

32. Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria

33. Bacteroids in a soybean root nodule.
5 µm
Bacteroids
within
vesicle
Nodules
Roots
Pea plant root.
Bacteroids in a soybean
root nodule.

34. Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell

35. The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen
Each legume species is associated with a particular strain of Rhizobium

36. LE 37-11 Rhizobium bacteria Dividing cells Infection in root cortex
thread
Dividing cells
in root cortex
Bacteroid
Dividing cells in
pericycle
Infected
root hair
Developing
root nodule
Bacteroid
Nodule
vascular
tissue
Bacteroid

37. 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

38. Symbiotic Nitrogen Fixation and Agriculture
Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation
A non-legume such as maize is planted one year, and the next year a legume is planted to restore the concentration of nitrogen in the soil

39. Mycorrhizae and Plant Nutrition
Mycorrhizae are mutualistic associations of fungi and roots
The fungus benefits from a steady supply of sugar from the host plant
The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption

40. The Two Main Types of Mycorrhizae
In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the surface of the root

41. LE 37-12a Epidermis Cortex Mantle (fungal sheath) 100 µm Endodermis
hyphae
between
cortical
cells
Mantle
(fungal sheath)
(colorized SEM)
Ectomycorrhizae.

42. In endomycorrhizae, microscopic fungal hyphae extend into the root

43. LE 37-12b Epidermis Cortex 10 µm Cortical cells Endodermis Fungal
hyphae
Vesicle
Casparian
strip
Root
hair
Arbuscules
(LM, stained specimen)
Endomycorrhizae.

44. Agricultural Importance of Mycorrhizae
Farmers and foresters often inoculate seeds with fungal spores to promote formation of mycorrhizae

45. Epiphytes, Parasitic Plants, and Carnivorous Plants
Some plants have nutritional adaptations that use other organisms in nonmutualistic ways
Video: Sun Dew Trapping Prey

46. LE 37-13a
Staghorn fern, and epiphyte. This tropical fern (genus Platycerium) grows on large rocks, cliffs, and trees. It has two types of fronds: branched fronds resembling antlers and circular fronds that form a collar around the base of the fern.

47. LE 37-13b Host’s phloem Dodder Haustoria
Mistletoe, a photosynthetic parasite.
Dodder, a nonphotosynthetic parasite.
Indian pipe, a nonphotosynthetic parasite.

48. LE 37-13c
Venus’ flytrap.
Pitcher plants.
Sundews.