Chapter 37

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

3. Figure 37.1 • The branching root system and shoot system of a vascular plant • Ensure extensive 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 • 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. 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

6. 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 • Researchers use hydroponic culture • To determine which chemicals elements are essential

7. Table 37.1 • Essential elements in plants

8. 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

9. Symptoms of Mineral Deficiency • The symptoms of mineral deficiency • Depend partly on the nutrient’s function • Depend on the mobility of a nutrient within the plant

10. 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

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

12. 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

13. Texture and Composition of Soils • Various sizes of particles derived from the breakdown of rock are found in soil • Along with organic material (humus) in various stages of decomposition • The eventual result of this activity is topsoil • A mixture of particles of rock and organic material

14. 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 • The topsoil and other distinct soil layers, or horizons • Are often visible in vertical profile where there is a road cut or deep hole

15. Soil particle surrounded by film of water 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 • After a heavy rainfall, water drains away from the larger spaces of soil • But smaller spaces retain water because of its attraction to surfaces of clay and other particles • The film of loosely bound water • Is usually available to plants

16. 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

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

18. Fertilizers • Commercially produced fertilizers • Contain minerals that are either mined or prepared by industrial processes • “Organic” fertilizers • Are composed of manure, fishmeal, or compost

19. Beginning phosphorus deficiency Well-developed phosphorus deficiency No phosphorus deficiency Figure 37.7 • 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

20. Irrigation • Irrigation, which is a huge drain on water resources when used for farming in arid regions • Can change the chemical makeup of soil

21. Erosion • Topsoil from thousands of acres of farmland • Is lost to water and wind erosion each year in the United States

22. Figure 37.8 • Certain precautions • Can prevent the loss of topsoil

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

24. Soil Reclamation • Some areas are unfit for agriculture • Because of contamination of soil or groundwater with toxic pollutants • A new method known as phytoremediation • Is a biological, nondestructive technology that seeks to reclaim contaminated areas

25. 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

26. 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

27. 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

28. 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

29. 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)

30. 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

31. 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

32. 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

33. 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

34. 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

35. Symbiotic Nitrogen Fixation and Agriculture • The agriculture benefits of symbiotic nitrogen fixation • Underlie crop rotation • In this practice • A non-legume such as maize is planted one year, and the following year a legume is planted to restore the concentration of nitrogen in the soil

36. 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

37. Epidermis Mantle(fungalsheath) Cortex 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. (a) 100 m Endodermis Fungalhyphaebetweencorticalcells Mantle(fungal sheath) (colorized SEM) The Two Main Types of Mycorrhizae • In ectomycorrhizae • The mycelium of the fungus forms a dense sheath over the surface of the root Figure 37.12a

38. Epidermis Cortex 10 m (b) 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. Cortical cells Endodermis Fungalhyphae Vesicle Casparianstrip Roothair Arbuscules (LM, stained specimen) Figure 37.12b • In endomycorrhizae • Microscopic fungal hyphae extend into the root

39. Agricultural Importance of Mycorrhizae • Farmers and foresters • Often inoculate seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae

40. Epiphytes, Parasitic Plants, and Carnivorous Plants • Some plants • Have nutritional adaptations that use other organisms in nonmutualistic ways

41. 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