Plant Nutrition: Essential Elements and Soil Conservation

1. Chapter 37 • Plant nutrition

2. 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. Figure 37.1 • The root system and shoot system • Ensure networking with both reservoirs of inorganic nutrients

4. 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 • Plants require certain chemical elements to complete their life cycle • Plants derive organic mass f/ CO2 • Also depend on soil nutrients e.g. water and minerals

6. Macronutrients and Micronutrients • More than 50 elements identified in plants, but not all are essential • Essential element is required for a plant to complete life cycle

7. 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 • Determines which chemicals elements are essential

8. Table 37.1 • Essential elements in plants

9. 9 essential elements are macronutrients (e.g. C,H,O,P,N,K) • Large amounts required • 8 are micronutrients (e.g.Fe) • Small amts. required

10. Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient Figure 37.4 Common deficiencies

11. Soil • Soil • Soil + climate • Major factors determining whether particular plants can grow well in a certain location • Texture • Soil’s general structure • Composition • Organic and inorganic chemical components

12. Particles derived from the breakdown of rock found in soil • Also organic material (humus) • Result is topsoil • A mixture ofparticles of rock and organicmaterial

13. The Ahorizon 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 • Topsoil + other distinct soil layers, or horizons

14. Soil particle surrounded by film ofwater Root hair Water available to plant 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. Figure 37.6a Film of loosely bound wateris usually available to plants

15. Soil Conservation and Sustainable Agriculture • In contrast to natural ecosystems • Agriculture depletes the mineral content of soil, taxes water reserves, and encourages erosion • Goal of soil conservation strategies Minimize damage

16. Fertilizers • Commercially produced fertilizers (N P K) • Minerals that are either mined or prepared by industrial processes • “Organic” fertilizers • e.g. manure, fishmeal, or compost

17. Beginning phosphorus deficiency Well-developed phosphorus deficiency No phosphorus deficiency Figure 37.7 • Agricultural research • Maintain crop yields while reducing fertilizer use • Genetically engineered “smart” plants • Inform the grower of nutrient deficiency

18. Irrigation • Huge drain on water resources in arid regions • Can change the chemical makeup of soil

19. Erosion • Topsoil from thousands of acres of farmland • Lost to water and wind erosion each year

20. Figure 37.8 • Prevention of topsoil loss

21. Goal of soil management • Sustainable agriculture, a variety of farming methods that are conservation-minded, e.g.No-till farming

22. Nitrogen often has the greatest effect on plant growth • Plants require nitrogen f/: • Proteins, nucleic acids, chlorophyll, others

23. Atmosphere N2 N2 Atmosphere Soil Nitrate and nitrogenousorganiccompoundsexported inxylem toshoot system 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 • Nitrogen-fixing bacteria convert atmospheric N2to form of N that plants can use

24. Two types of relationships plants have with other organisms are mutualistic • Symbiotic nitrogen fixation (Rhizobium) • Mycorrhizae

25. Symbiotic N2 Fixation • Provide plant w/ a built-in source of fixed N2 • Legume family (e.g. peas, beans)

26. 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 • Root nodules • Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria

27. Each legume • Is associated with a particular strain of Rhizobium

28. 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. Dividing cellsin root cortex 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 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 The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant. 4 Nodulevasculartissue Bacteroid • Development of a soybean root nodule Figure 37.11

29. Crop rotation •  Non-legume (e.g corn) planted one year, following year legume is planted

30. Mycorrhizae • Mycorrhizae • Mutualistic associations of fungi and roots • Fungussteady supply of sugar f/ plant • In return, the fungus increases the surface area of water uptake

31. Epidermis Cortex (a) 100 m Mantle(fungalsheath) aEctomycorrhizae. 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. Endodermis Fungalhyphaebetweencorticalcells Mantle(fungal sheath) (colorized SEM) Mycorrhizae Figure 37.12a

32. Epidermis Cortex (b) 10 m Cortical cells 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. Endodermis Fungalhyphae Vesicle Casparianstrip Roothair Arbuscules (LM, stained specimen) Figure 37.12b Mycorrhizae

33. Epiphytes, Parasitic Plants, and Carnivorous Plants • Nutritional adaptations that use other organisms in nonmutualistic ways

34. 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