1. Chapter 37
Plant Nutrition

2. 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

3. 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

4. Essential elements in plants
Table 37.1

5. 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

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

7. 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

8. 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 –

9. 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

10. 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

11. 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

12. 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)

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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