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Final Soil Fertility > Rhizosphere 2 > Flashcards

Rhizosphere 2 Flashcards

1
Q

Rhizodeposition

A

is the release of organic carbon from the root system to the rhizosphere

  • annual species-40% of C allocated to roots
  • Forest trees-70% or more of C
  • increases when plants are under stress
  • increases microorganism activity as more C substrate is available
  • low molecular weight organic exudates include organic acids.
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2
Q

root exudates

A
  • high molecular weight solutes

- low molecular weight solutes

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3
Q

high molecular weight solutes

A
  • mucilage

- ectoenzymes

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4
Q

low molecular weight solutes

A
  • organic acids
  • sugars
  • phenolic compounds
  • amino acids
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5
Q

Major components of plant root exudates

A

Sugars: Glucose, Fructose, Maltose,

Amino Acids: Valine, Leucine, serine

Organic acids: Oxalate, Malate, acetate

Others: flavones, adenine, Guanine

Proteins/Enzymes: Invertase, Amylase, Protease

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6
Q

Quantities of Exudates

A
  • Increase when plant roots are experiencing high bulk densities (cereal plants: 5% of root dry weight were exudates when plants grown in nutrient solution, 9% when grown in glass bead substrate)
  • Increases when plant experiences mineral nutrient deficiencies
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7
Q

Release of Organic material (rhizodeposition): Amounts and composition are affected by:

A
  • Plant species and age
  • Soil type and properties
  • Nutritional status of the plant
  • temperature
  • light intensity and duration
  • Presence of microorganisms
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8
Q

Main sites of root exudation

A

-spike at apex of root system and at point where lateral roots come off of a root system we have increases in root exudates

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9
Q

Mucilage def:

A

high-molecular weight gelatinous material that covers roots in the apical zones

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10
Q

Mucilage

A
  • consists mainly of polysaccharides
  • positively correlated with root growth rate
  • secreted by the root cap cells and released by epidermis cells
  • colonized by microorganisms
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11
Q

Mucigel

A

mixture of gelatinous material, microorganisms, and soil particles

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12
Q

Mucilage functions

A
  • protection of root apical zones from desiccation
  • lubrication of the root as it moves through soil
  • influence ion uptake
  • improving the soil-root contact
  • aggregation of soil particles
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13
Q

Low-molecular weight root exudates: Main compounds

A
  • sugars
  • organic acids
  • phenolic compounds
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14
Q

Low-molecular weight root exudates

A

principle reactions involve mineral nutrient mobilization in the rhizosphere
-insoluble nutrient containing compounds in soil are solubilized

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15
Q

Plant exudates and plant nutritional status

A

Plants are nutrient deficient:

  • quantity of root exudates increases
  • composition of exudates changes

ex. K deficiency of maize
- amount of exudates increases
- organic acids increase to solubilize and exchange limited soil K.

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16
Q

Ectoenzymes

A

root borne enzymes such as acid phosphatases (increase in relation to deficiencies, i.e. P deficiency)

  • important to extraction and P uptake on low P soils
  • Many enzymes located in the root apoplasm and influence mineral nutrition of plants in low nutrient status soil situations
17
Q

Mycorrhizas

A
  • most widespread association between microorganisms and plants-80-90%
  • fungus is strongly or wholly dependent on the higher plant (Mutualistic, neutral, or parasitic)
18
Q

Non-mycorrhizal plants

A
  • very dry or saline soils
  • waterlogged (submerged soils)
  • severely disturbed soils
  • severely disturbed soils
  • soil fertility is extremely high or low
19
Q

Symbiosis Plant: Plant interactions

A
  • Nitrogen Fixing (certain species)
  • Mycorrhizas (nearly all plants)
  • Endophyte (antifeedant in grasses) (Acremonium on fescue, and ryegrass)
20
Q

Roots: Ectomycorrhizas

A
  • swollen, forked fine roots,
  • fungal mantle
  • harting net
  • no intracellular hyphae
21
Q

Roots: Endomycorrhizas

A
  • no obvious external root modification
  • no mantle or harting net
  • Extensive intracellular hyphae
  • Presence of arbusucles, vesicles, and chlamydospores
22
Q

Mycorrhizas and mineral nutrition: Vesicular-Arbuscular Mycorrhizas (VAM)

A
  • improve supply of low mobility mineral nutrients, mostly phosphorus
  • External hyphae absorb P outside the root depletion zone of nonmycorrhizal roots
  • uptake rate of P per unit root length in 2-3 times greater than nonmycorrhizal plants
23
Q

Ectomycorrhizas

A

-structurally different from VAM
-Fungal Sheath surrounding the apical root zone (varies with plant species, season, and environmental conditions)
-important for P nutrition at low soil P levels
Several specific differences and plant responses are discussed in text

24
Q

Mycorrhizas: Practical Implications

A
  • Enhanced P availability in low P soils
  • Feasible to inoculate plants, i.e., forest tree seedlings, to improve early growth (Possible with ECM fungi, limited VAM inoculation success)
  • high fertility level agronomic and horticultural crop production, not of great importance
  • Natural ecosystem studies, always consider
25
Q

Strigolactone is produced from ____

A

carotenoids

these hormones and signals are produced in the roots in response to low phosphate conditions or high auxin flow from the shoot

26
Q

Strigolactones is produced….

A

at the base of the root and sent throughout the roots to attract fungi and prevent lateral growth

27
Q

Strigolactones roles

A
  • involved in promoting germination in root-parasitic plants
  • plays a role in attracting mycorrhizal fungi to the root
  • suppress lateral shoot branching and promotes apical dominance
28
Q

Roots: Symbiont Inoculation

A
  • spores
  • mycelium
  • inoculated roots
29
Q

Nitrogen Fixation

A
  • Rhizobium + legumes
  • Frankia + various families
    • Russian Olive
    • Alder
    • Mt. mahogany
30
Q

Nitrogen Fixation

A
  • Globally, 140 billion kg N fixed/yr by symbiotic organisms
  • atmosphere=78% N2
  • Convert N2 gas into amino acids
  • Legumes + Bacteria (rhizobium)
  • Alder + Actinomycete (Frankia)
  • Cycads + Blue green algae (Nostoc)

Final Soil Fertility (4 decks)

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