Plant Nutrition: Essential Elements and Soil Interactions

1. Chapter 37 Plant Nutrition

2. Figure 37.1 Root and shoot systems of a pea seedling

3. H2O CO2 CO2, the source of carbon for Photosynthesis, diffuses into leaves from the air through stomata. O2 Through stomata, leaves expel H2O and O2. Roots take in O2 and expel CO2. The plant uses O2 for cellular respiration but is a net O2 producer. O2 Minerals Roots absorb H2O and minerals from the soil. CO2 H2O Figure 37.2 The uptake of nutrients by a plant: a review

4. APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants. 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. Control: Solution containing all minerals Experimental: Solution without potassium 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. Figure 37.3 Hydroponic Culture

5. Table 37.1 Essential Elements in Plants

6. Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient Figure 37.4 The most common mineral deficiencies, as seen in maize leaves

7. The A horizon is the topsoil, a mixture of broken-down rock of various textures, living organisms, and decaying organic matter. A The B horizon contains much less organic matter than the A horizon and is less weathered. B C The C horizon, composed mainly of partially broken-down rock, serves as the “parent” material for the upper layers of soil. Figure 37.5 Soil horizons

8. Soil particle surrounded by film of water Soil particle – – K+ Root hair K+ – – – – – – – Water available to plant Ca2+ Mg2+ Cu2+ K+ H+ H2CO3 HCO3– + H2O + CO2 H+ Root hair Air space (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. (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. Figure 37.6 The availability of soil water and minerals

9. No phosphorus deficiency Beginning phosphorus deficiency Well-developed phosphorus deficiency Figure 37.7 Deficiency warnings from “smart” plants

10. Figure 37.8 Contour tillage

11. Atmosphere N2 Atmosphere Soil Nitrogen-fixingbacteria N2 H+ (from soil) NH3 (ammonia) Soil NH4 + (ammonia) Organicmaterial (humus) Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (layer 1) Ammonifyingbacteria

12. Atmosphere N2 N2 Atmosphere Soil Nitrogen-fixingbacteria N2 Denitrifyingbacteria H+ (from soil) NH3 (ammonia) Soil NO3 – (nitrate) NH4 + (ammonia) Nitrifyingbacteria Organicmaterial (humus) Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (layer 2) Ammonifyingbacteria

13. Atmosphere N2 N2 Atmosphere Nitrate and nitrogenousorganiccompoundsexported inxylem toshoot system Soil Nitrogen-fixingbacteria N2 Denitrifyingbacteria H+ (from soil) NH4 + NH3 (ammonia) Soil NO3 – (nitrate) NH4 + (ammonia) Nitrifyingbacteria Organicmaterial (humus) Root Figure 37.9 The role of soil bacteria in the nitrogen nutrition of plants (layer 3) Ammonifyingbacteria

14. 5 m Bacteroids within vesicle Nodules Roots (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. (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 37.10 Root nodules on legumes

15. Rhizobiumbacteria Infectionthread 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. 1 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. Dividing cellsin root cortex Bacteroid Dividing cells in pericycle Infectedroot hair 1 2 Developingroot nodule Bacteroid 3 3 Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse, forming the nodule. 4 4 The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant. Nodulevasculartissue Bacteroid Figure 37.11 Development of a soybean root nodule

16. Mantle(fungalsheath) Epidermis Cortex 1Ectomycorrhizae. 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. 100 m Endodermis Fungalhyphaebetweencorticalcells Mantle(fungal sheath) (colorized SEM) 2Endomycorrhizae. 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. Epidermis Cortex 10 m Cortical cells Endodermis Fungalhyphae Vesicle Casparianstrip Roothair Arbuscules (LM, stained specimen) Figure 37.12 Mycorrhizae

17. EPIPHYTES Staghorn fern, an epiphyte PARASITIC PLANTS Host’s phloem Dodder Haustoria Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite Indian pipe, a nonphotosynthetic parasite CARNIVOROUS PLANTS Venus’ flytrap Sundews Pitcher plants Figure 37.13 Unusual Nutritional Adaptations in Plants

18. 37.13 Sun Dew Trap Prey