Soil and Plant Nutrition - Fundametnals of Biology - Lecture Notes, Study notes for Biology. Avinashilingam University

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Description: These are the lecture notes of Fundametnals of Biology. Key important points are: Soil and Plant Nutrition, Macronutrients and Micronutrients, Symptoms of Mineral Deficiency, Genetic Modification, Resistance to Aluminum Toxicity, Flood Tolerance, Soil Bacteria
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got a great help in learning about macronutrients

23/04/13 12:54
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1 Chapter 37 Soil and Plant Nutrition

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3 Concept 37.2: Plants require essential 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

4 Macronutrients and Micronutrients • More than 50 chemical elements have been identified among the inorganic substances

in plants, but not all of these are essential to plants • A chemical element is considered an essential element if it is required for a plant to

complete its life cycle • Researchers use hydroponic culture to determine which chemical elements are

essential

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• Nine of the essential elements are called macronutrients because plants require them in relatively large amounts

• The macronutrients are carbon, oxygen, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, and magnesium

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• The remaining eight are called micronutrients because plants need them in very small amounts

• The micronutrients are chlorine, iron, manganese, boron, zinc, copper, nickel, and molybdenum

9 Symptoms of Mineral Deficiency • Symptoms of mineral deficiency depend on the nutrient’s function and mobility within

the plant • 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 • The most common deficiencies are those of nitrogen, potassium, and phosphorus

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11 Improving Plant Nutrition by Genetic Modification: Some Examples • Genetic engineering can improve plant nutrition and fertilizer usage

12 Resistance to Aluminum Toxicity • Aluminum in acidic soils damages roots and greatly reduces crop yields • The introduction of bacterial genes into plant genomes can cause plants to secrete

acids that bind to and tie up aluminum

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13 Flood Tolerance • Waterlogged soils deprive roots of oxygen and cause buildup of ethanol and toxins • The gene Submergence 1A-1 is responsible for submergence tolerance in flood-

resistant rice

14 Smart Plants • “Smart” plants inform the grower of a nutrient deficiency before damage has occurred • A blue tinge indicates when these plants need phosphate-containing fertilizer

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16 Concept 37.3: Plant nutrition often involves relationships with other organisms • Plants and soil microbes have a mutualistic relationship

– Dead plants provide energy needed by soil-dwelling microorganisms – Secretions from living roots support a wide variety of microbes in the near-root

environment

17 Soil Bacteria and Plant Nutrition • The layer of soil bound to the plant’s roots is the rhizosphere • The rhizosphere has high microbial activity because of sugars, amino acids, and

organic acids secreted by roots

18 Rhizobacteria • Free-living rhizobacteria thrive in the rhizosphere, and some can enter roots • Rhizobacteria can play several roles

– Produce hormones that stimulate plant growth – Produce antibiotics that protect roots from disease – Absorb toxic metals or make nutrients more available to roots

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• Inoculation of seeds with rhizobacteria can increase crop yields

20 Bacteria in the Nitrogen Cycle • Nitrogen can be an important limiting nutrient for plant growth • The nitrogen cycle transforms nitrogen and nitrogen-containing compounds • Most soil nitrogen comes from actions of soil bacteria

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• Plants absorb nitrogen as either NO3– or NH4+ • Bacteria break down organic compounds or use N2 to produce NH3, which is converted

to NH4+ • Nitrification is carried out by bacteria that convert NH3 into NO3–

23 Nitrogen-Fixing Bacteria: A Closer Look • N2 is abundant in the atmosphere, but unavailable to plants • Nitrogen fixation is the conversion of nitrogen from N2 to NH3 • Symbiotic relationships with nitrogen-fixing bacteria provide some plant species with a

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built-in source of fixed nitrogen • Key symbioses occur between nitrogen-fixing bacteria and plants, including those in

the legume family (peas, beans, and other similar plants)

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• Along a legume’s roots are swellings called nodules, composed of plant cells “infected” by nitrogen-fixing Rhizobium bacteria

• Inside the root nodule, Rhizobium bacteria assume a form called bacteroids, which are contained within vesicles formed by the root cell

• The bacteria of a root nodule obtain sugar from the plant and supply the plant with fixed nitrogen

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• Each legume species is associated with a particular strain of Rhizobium • The development of a nitrogen-fixing root nodule depends on chemical dialogue

between Rhizobium bacteria and root cells of their specific plant hosts

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28 Nitrogen Fixation and Agriculture Crop rotation takes advantage of the agricultural benefits of symbiotic nitrogen fixation • A non-legume such as maize is planted one year, and the next year a legume is

planted to restore the concentration of fixed nitrogen in the soil

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• Instead of being harvested, the legume crop is often plowed under to decompose as “green manure” and reduce the need for manufactured fertilizer

• Non-legumes such as alder trees, certain tropical grasses, and rice benefit either directly or indirectly from nitrogen-fixing bacteria

30 Fungi and Plant Nutrition Mycorrhizae are mutualistic associations of fungi and roots • The fungus benefits from a steady supply of sugar from the host plant • The host plant benefits because the fungus increases the surface area for water

uptake and mineral absorption • Mycorrizal relationships are common and might have helped plants to first colonize

land

31 The Two Main Types of Mycorrhizae • In ectomycorrhizae, the mycelium of the fungus forms a dense sheath over the

surface of the root • These hyphae form a network in the apoplast, but do not penetrate the root cells

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• In arbuscular mycorrhizae, microscopic fungal hyphae extend into the root • These mycorrhizae penetrate the cell wall but not the plasma membrane to form

branched arbuscules within root cells

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35 Agricultural and Ecological Importance of Mycorrhizae • Farmers and foresters often inoculate seeds with fungal spores to promote formation of

mycorrhizae • Some invasive exotic plants disrupt interactions between native plants and their

mycorrhizal fungi

36 Epiphytes, Parasitic Plants, and Carnivorous Plants • Some plants have nutritional adaptations that use other organisms in nonmutualistic

ways • An epiphyte grows on another plant and obtains water and minerals from rain

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• Parasitic plants absorb sugars and minerals from their living host plant

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• Carnivorous plants are photosynthetic but obtain nitrogen by killing and digesting mostly insects

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