ch. 37 soil & plant nutrition - pride through excellence substance that makes up most of dry...
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1Feb 104:02 PM
Ch. 37Soil &
Plant Nutrition
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Essential Question:
How do nutrients affect plant growth?
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a. Mineral nutrients: inorganic ions found in soil that plants use for growth
ex. nitrogen in form of nitrate
b. water 8090% of plantgives hydrogen and some oxygen to plantmost is lost in transpirationfunctions:
1. solvent2. volume for cell elongation3. keeps cell turgid
c. carbon dioxide from airorganic substance that makes up most of dry matter is carbohydratesmost abundant elements are C, H, O
Needed for plants to grow:
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Essential elements (nutrient) chemical that is required by plant to complete life cycle and reproduce
researchers use Hydroponics to study the effect of chemicals on plants
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macronutrients elements that plants require in large amountsex. carbon, oxygen, hydrogen, nitrogen, potassium, Calcium,
magnesium,phosphorus, sulfurmakes up major organic compoundsEx. magnesium is component in chlorophyll, activates enzymes
deficiencies usually occur with phosphorus, potassium, nitrogen
Micronutrients elements that plants require in small amounts ex. chlorine, iron, manganese, boron, zinc, copper, nickel, and
molybdenummake cofactors nonprotein helpers in enzyme reactions
Ex. iron for cytochromes in ETC molybdenum for nitrate reduction to make nitrate ions
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dependent on function:1. deficiency in magnesium causes chlorosis (yellowing of leaves)2. deficiency in iron also causes chlorosis involved in chlorophyll synthesis
Magnesium deficiency in tomato plant
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dependent on mobility in plantif nutrient moves easily, deficiency shows up in older tissue first
young tissue gets first dibs on nutrientsEx. magnesium shows chlorosis in older leaves first
if nutrient is immobile, shows up in younger tissue firstEx. iron (slow) yellowing young leaves
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most common deficiencies:nitrogenphosphoruspotassium
to diagnose deficiencies analyze plant and soil
Can use hydroponics to get optimal nutrition and regulationdisadvantage expensive
nitrogen is the most limiting to plant growth.
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Nitrogen Fixation
atmosphere = 78% nitrogen but not in useable plant form
useable form is nitrate, so atmospheric nitrogen has to be converted to ammonium and then to nitrate (comes from decay of humus by bacteria)
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bacteria for nitrogen fixation are either found in soil or plant root nodules (symbiosis)
nitrifying bacteria produce nitrate by oxidizing ammonium
root nodules
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Role of bacteria in symbiotic nitrogen fixation
happens in legume family (peas, beans, alfalfa, peanuts, clover)
root nodules contain nitrogen fixing Rhizobium bacteriaRhizobium form bacteroids
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Rhizobium uses atmospheric nitrogen and change it to ammonium used by plant
symbiosis provides right amount of fertilizer without farmer having to fertilize saves $
each legume is associated with a specific Rhizobium strain mutualistic relationship:
plant gets nitrogen from bacteriabacteria get carbohydrates and organic compounds from
plant
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1. plant secretes flavenoids that certain strains of Rhizobium detect and absorb2. activates a gene regulating protein in bacterium and which on genes (nod) to make nodule3. Nod factors from bacteria signal root to let Rhizobium enter and form the nodule
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"Super" varieties of plants have more protein than normal
disadvantage high demand for nitrogen so need high fertilizer use
consumes lots of energy (fossil fuels)
poor countries need high protein crops, but not able to afford them
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crop rotation
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Mycorrhizae associations between fungi and roots (mutualistic)
fungus gets supply of sugar
plant gets increased surface area for water and mineral uptake, growth factors from fungus which help lengthen the roots and antibiotics to prevent pathogens
scientists believe this relationship helped plants evolve to become land plants
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two types of mycorrhizae:1. ectomycorrhizae mycelium forms mass over surface of root and grow into root apoplast (extracellular space)
usually don't form root hairsex. pines, spruce, oak, walnut, willow, beech
2. endomycorrihizae no dense mass, hyphae extend inwards• form arbuscles (branched invaginations of hyphae)• found in 90% of plants
ex. corn, wheat, legumes
2. endomycorrhizae fine hyphae from soil into root cells and grow tube that invaginates a root cell
arbuscles branched structures for nutrient transferfound in 85% of plant species
fungal sheath
ectomycorrihizae endomycorrihizae
arbuslces
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epiphytes plants that live on other plants, but get their own nutrients usually through their leaves, not rootsex. orchids, staghorn ferns
Other relationships in plants
http://www.rbgkew.org.uk/ksheets/epiphytes.html
staghorn fern in Floridahttp://www.floridaplants.com/hort_epiphytes.htm
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Parasitic plants live on a host and absorb sugars and mineralsex. mistletoe, dodder, Indian pipe
Indian Pipe
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Carnivorous plants photosynthetic plants, but get some nitrogen and minerals by killing insects and digesting them. Usually live inacid bogs
ex. Venus Fly trap, Pitcher plant, sundews
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Soil's texture and composition will change depending on where they are found, so nutrients will change too.
texture = particle size (sand, silt, clay)composition = organic and inorganic chemical components
soil is formed by rock weathering (freezing, acids, mechanical fracturing
topsoil mixture of particles from rock, living organisms, and humus(remains of partially decayed organic matter)
humus prevents clay from packing together, builds crumbly soil for aerationhas minerals when microorganisms breakdown organic
material
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soil is arranged in horizons (layers)
A horizon = topsoil, richest and most important for plant growthloam made of equal amounts of sand, silt and clay
clay for large surface areasand provide air spaces (oxygen for cellular respiration)
not enough air = suffocation by water, mold attack on roots
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Topsoil includes organisms (5 billion bacteria, worms, insects, algae, fungi)earthworms add air to soil, add mucus to hold particles togetherbacteria use nitrogen fixation, alter mineral compositionroots prevent erosion
Roots take in a soil solution made of water and dissolved minerals (ions)
some particles are bound tightly to soil due to chargeanions: nitrate, phosphate, and sulfate are not bound
tightly easily released from soilleached from soil during rainstorms
cations: potassium, Calcium and magnesium are bound to soil particles
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Cation exchange Hydrogen ions made by secretion of root hairs and cellular respiration replace cations attached to soil, so they can then be absorbed by root
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Soil Conservation and Sustainable Agriculture
soil mismanagementEx. "dustbowl" in 1930' s in U.S.
caused by overgrazing of cattle, wheat crops instead of grasses, drought left topsoil exposed
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agriculture depletes nutrients in soiluse fertilizers to replace lost nutrients
farmers also need to irrigate crops
Soil conservation goals:irrigate properlyfertilize properlyprevent erosion
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Fertilizers
three ingredients:nitrogen (as ammonium or nitrate), phosphorus (as phosphoric
acid), potassium (potash)NPK ratio ex. 15105
organic fertilizers= manure, fishmeal, compost
excess minerals not taken up by roots are leached away, can pollute water
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soil pH influences uptake of mineralsat certain pH's some minerals absorbed, others notif acidic can add calcium carbonate or calcium hydroxideif alkaline add sulfatein tropical areas, soil is acidic, aluminum dissolves and is toxic to roots plants can secrete organic ions to bind with Al and make it harmless
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Irrigationdiversion of water from rivers is major issueirrigation in arid areas, makes soil salty infertiletypes of irrigation:
overhead drip
http://ga.water.usgs.gov/edu/irdrip.html
furrow
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Erosion movement of soil from one place to another
two main causes: water and wind
to prevent erosion:1. windbreaks planting trees surrounding the fields to prevent wind erosion
2. contouring pattern
3. terracinghttp://www.unl.edu/nac/windbreaks.htm
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sustainable agriculturelong term productive farming practices that are environmentally safe
Soil reclamation reclaiming soil that has been contaminated with heavy metals or organic pollutants
for soil 1. can remove contaminated soil and store in landfill2. phytoremediation use of plants to extract soil
pollutants and concentrating them into plant tissue and then disposedex. alpine pennycress collects zinc in shoots (300x most
plants)
33Apr 28:51 AM