Chapter 37: Soil and Plant Nutrition

Chapter 37 Soil and Plant Nutrition Q&A Ex: Genlisea uses underground leaves to capture soil organisms. Notes Corkscrew Carnivore: Plants that live in nutrient poor soils Use camery to obtain minerals Soil-a fragile complex ecosystem Plants use top layers for water & minerals Living organisms play an important role in soil layers Physical properties: Composition & Texture Soil texture: Particles by size: SAND Silt clay →Topsoil (A horizon): minerals, decaying organic material, humus, living organisms Sandy soils don't retain enough water to support Plant growth Clay soil retains too much Soil solution: water, dissolved minerals in the pores between soil particles After rainfall: water drains from ↑ spaces in the soil to spaces retain water due to adhesion to particles Loams: most fertile topsoil contain equal: Sand, Silt, clay Topsoil composition Inorganic: Cations **Organic Chemical Components** Humus builds a complex Topsoil: Bacteria, fungi, algae nematodes, earthworms Help decompose organic material & mix the soil Cation exchange in soil Mineral cations are released. H2O reacts with H+ H+ Ca Mg K Ca Mg K Root hair Q&A Notes Soil Conservation and Sustainable Agriculture Soil management by fertilization + other practices allows for agriculture activities American Dust Bowl of 1930s resulted from soil mismanagement In contrast with natural ecosystems, agriculture → depletes the mineral content of soil → encourages erosion At present: 30% of world's farmland has low productivity because of soil mismanagement Sustainable Agriculture goal: use farming methods that are conservation-minded, environmentally sound, and profitable Plants Require Essential Elements to complete their life cycle 90-96% of dry mass is water 4% of dry mass is CO2 assimilated into carbohydrates (during photosynthesis) 1% of dry mass is inorganic substances from soil Essential Elements 50 chemical elements have been identified in plants (not all are essential) Remember These: → There are 17 essential elements → chemical elements are required for a plant to complete its life cycle and reproduce 9 essential elements are Macronutrients (needed in LARGE amounts) Carbon, Oxygen, Hydrogen, Nitrogen, Phosphorus, Sulfur, Potassium, Calcium, Magnesium 8 are Micronutrients (small amounts) Chlorine, Iron, Manganese, Boron, Zinc, Copper, Nickel, Molybdenum → function as cofactors, non-protein helpers in enzymatic reactions Q&A Notes Symptoms of Mineral Deficiency Depend on the nutrient's function Most Common: Nitrogen, Potassium, Phosphorus Plant Nutrition (often) Involves Relationships with Other Organisms Plants & soil = mutualistic relationship → Dead plants provide energy through soil-dwelling microorganisms → Secretions from living roots support a variety of microbes in the near-root environment Bacteria and Plant Nutrition Rhizosphere = layer of soil surrounding the plant's roots (close up) → Free-living bacteria in it are Rhizobacteria Endophytes = nonpathogenic bacteria that live between the cells of plant tissues → Endophytes & Rhizobacteria depend on nutrients secreted by plant cells → In return, help enhance plant growth * → Producing: Chemicals → Promote plant growth * → Antibiotics → Protects roots from disease → Absorbing: Toxic metals * → Increases nutrient availability Bacteria in the Nitrogen Cycle Nitrogen = limiting nutrient for plant growth Nitrogen absorbed as Nitrate (NO3-) or Ammonia (NH4+) Nitrogen Source: actions of soil bacteria Nitrogen Cycle: Nitrogen & nitrogen-containing compounds Transformations - thus Q&A Notes Nitrogen is lost to the atmosphere when denitrifying bacteria convert NO3- to N2 Nitrogen Fixing Bacteria (Closer look) Nitrogen is abundant in the atmosphere, but unavailable to plants because of the triple bond between atoms in N2 Nitrogen fixation:1 conversion of N2 to NH3 N2 + 8e- + 8H+ + 16 ATP → 2NH3 + H2 + 16 ADP + 16 Pi   Symbiotic relationships (w/ N-fixing Rhizobium bacteria) can provide: a fixed source of Nitrogen Nodules: Swellings along a legume's roots Composed of: Plant cells Infected by: Rhizobium bacteria Inside: Rhizobium assume the form: bacteroids contained in: vesicles formed by: root cell Nitrogen Fixation & Agriculture Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation Non-legume (maize or wheat) Planted one year Legume (beans or peas) Planted the following year Preserves nitrogen-enriched soil Fungi & Plant Nutrition Mycorrhizae = mutualistic associations of fungi & roots Fungus benefits → steady supply of sugar & mineral absorption Host plant benefits → fungus ↑ uptake & mineral absorption Mycorrhizae fungi → stimulate root growth & branching Q&A Notes Agricultural & Ecological Importance of Mycorrhizae Farmers & Foresters: Inoculate seeds with fungal spores → Promote formation of Mycorrhizal associations Some invasive exotic plants disrupt interactions between native plants & their mycorrhizal fungi Epiphytes, Parasitic Plants, Carnivorous Plants Some plants have nutritional adaptations that use other organisms in nonmutualistic ways 3 unusual adaptations: Epiphytes: Grow on another plant + obtain water/minerals from rain Staghorn fern Parasitic Plants: Absorb Sugars & Minerals from living host Mistletoe, Rafflesia, Indian Pipe PS: Non PS: PS of mycorrhizae Carnivorous Plants: Obtain Nitrogen by killing & digesting insects Sundew, Pitcher Plant, Venus Fly-traps