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Chapter 37 • Plant nutrition Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • The root system and shoot system – Ensure networking with both reservoirs of inorganic nutrients Figure 37.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 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 Figure 37.2 Roots absorb H2O and minerals from the soil. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings CO2 H2O Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Hydroponic culture – Determines which chemicals elements are essential 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 Figure 37.3 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Essential elements in plants Table 37.1 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Common deficiencies Healthy Phosphate-deficient Potassium-deficient Nitrogen-deficient ure 37.4 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Particles derived from the breakdown of rock found in soil – Also organic material (humus) • Result is topsoil – A mixture of particles of rock and organic material Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Topsoil + other distinct soil layers, or horizons A horizon The is the topsoil, a mixture of broken-down rock of various textures, living organisms, and decaying organic matter. A B C B horizon The contains much less organic matter than the A horizon and is less weathered. C horizon The , composed mainly of partially broken-down rock, serves as the “parent” material for the upper layers of soil. Figure 37.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Film of loosely bound water is usually available to plants Soil particle surrounded by film of water Root hair Water available to plant Air space Figure 37.6a (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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Agricultural research – Maintain crop yields while reducing fertilizer use • Genetically engineered “smart” plants – Inform the grower of nutrient deficiency No phosphorus deficiency Figure 37.7 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Beginning phosphorus deficiency Well-developed phosphorus deficiency Irrigation • Huge drain on water resources in arid regions – Can change the chemical makeup of soil Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Erosion • Topsoil from thousands of acres of farmland – Lost to water and wind erosion each year Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Prevention of topsoil loss Figure 37.8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Goal of soil management – Sustainable agriculture, a variety of farming methods that are conservation-minded, e.g. No-till farming Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Nitrogen often has the greatest effect on plant growth • Plants require nitrogen f/: – Proteins, nucleic acids, chlorophyll, others Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Soil Bacteria • Nitrogen-fixing bacteria convert atmospheric N2 to form of N that plants can use Atmosphere N2 N2 Atmosphere Soil N2 Nitrogen-fixing bacteria Denitrifying bacteria H+ (From soil) Soil + NH4 NH3 (ammonia) – + NH4 (ammonium) Organic material (humus) Nitrate and nitrogenous organic compounds exported in xylem to shoot system Nitrifying bacteria NO3 (nitrate) Ammonifying bacteria Figure 37.9 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Root • Two types of relationships plants have with other organisms are mutualistic – Symbiotic nitrogen fixation (Rhizobium) – Mycorrhizae Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Symbiotic N2 Fixation • Provide plant w/ a built-in source of fixed N2 • Legume family (e.g. peas, beans) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Root nodules – Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria Nodules Roots Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Each legume – Is associated with a particular strain of Rhizobium Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Development of a soybean root nodule 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. Infection thread Rhizobium bacteria Dividing cells in root cortex Bacteroid Infected root hair Dividing cells in pericycle 1 2 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 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. Bacteroid Figure 37.11 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bacteroid Nodule vascular tissue • Crop rotation • Non-legume (e.g corn) planted one year, following year legume is planted Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mycorrhizae Epidermis (a) a Ectomycorrhizae. 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. Cortex Mantle (fungal sheath) 100 m Endodermis Mantle (fungal sheath) Fungal hyphae between cortical cells (colorized SEM) Figure 37.12a Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mycorrhizae Epidermis (b) Cortex Cortical cells 2 Endomycorrhizae. 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. 10 m Endodermis Fungal hyphae Vesicle Casparian strip Root hair Arbuscules (LM, stained specimen) Figure 37.12b Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Epiphytes, Parasitic Plants, and Carnivorous Plants • Nutritional adaptations that use other organisms in nonmutualistic ways Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings • Exploring unusual nutritional adaptations in plants 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 Figure 37.13 Venus’ flytrap Pitcher plants Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sundews