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

Biology

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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1Chapter 37
Soil and Plant Nutrition
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3Concept 37.2: Plants require essential elements to complete their life cycle
Plants derive most of their organic mass from the CO2of air, but they also depend on
soil nutrients such as water and minerals
4Macronutrients 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
9Symptoms 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 NO3or NH4+
Bacteria break down organic compounds or use N2to 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
N2is abundant in the atmosphere, but unavailable to plants
Nitrogen fixation is the conversion of nitrogen from N2to 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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khattak - Virtual University of Pakistan

got a great help in learning about macronutrients

23/04/13 12:54
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