Plant Nutrition and Soil Quality: Essential Elements and Nutritional Adaptations

1. Chapter 37 Plant Nutrition

2. 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 • 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

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. Table 37.1 • Essential elements in plants

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

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. Soil particle – – K+ K+ – – – – – – – Ca2+ Mg2+ Cu2+ K+ H+ HCO3– + H2CO3 H2O + CO2 H+ Root hair (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 hairsand 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 37.6b • Acids derived from roots contribute to a plant’s uptake of minerals • When H+ displaces mineral cations from clay particles

9. 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. 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+ (ammonium) Nitrifyingbacteria Ammonifyingbacteria Organicmaterial (humus) Root Figure 37.9 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

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

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 froma root nodule of soybean is filledwith 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. Rhizobiumbacteria Infectionthread Dividing cellsin root cortex 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. Bacteroid Dividing cells in pericycle Infectedroot hair 1 2 Developingroot nodule Bacteroid 3 3Growth 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 • Development of a soybean root nodule Figure 37.11

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