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Final Soil Fertility > Rhizosphere > Flashcards

Rhizosphere Flashcards

1
Q

Rhizosphere

A

narrow region of soil that is directly influenced by root secretions and associated soil microorganisms

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2
Q

Endorhizosphere

A

portions of the cortex and endodermis in which microbes and cations can occupy the “free space” between cells (apoplastic space)

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3
Q

apoplastic space

A

free space between cells

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4
Q

Rhizoplane

A

the medial zone directly adjacent to the root including the root epidermis and the mucilage

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5
Q

Ectorhizosphere

A

extends from rhizoplane out into the bulk soil

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6
Q

The rhizosphere is not

A

a defined size or shape

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7
Q

The rhizosphere consists of

A

a gradient in chemical, biological and physical properties which change both radially and longitudinally along the root

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8
Q

gradients at the rhizosphere

A 
nutrient concentration
pH
Redox potential 
Exudates
Microbial activity
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9
Q

Microbial activity

A

non-infecting rhizosphere microorganisms

infecting rhizosphere microorganisms: VA mycorrhiza, ectomycorrhiza

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10
Q

roots are a _____ for _____ and ______

A

sink

nutrients and water

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11
Q

nutrient ions and other ions may be _________ or _______ at the root surface

A

accumulated or depleted

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12
Q

roots release ____ or ____

A

H+ or HCO3-

Changes pH

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13
Q

Oxygen consumed or released…..

A

alters redox potential

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14
Q

Redox potential

A

A measure of electrochemical potential or electron availability within a system

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15
Q

electrons are essential to…..

A

all inorganic and organic reactions

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16
Q

Redox potential predicts..

A

stability of various compounds that regulate nutrients and metal availability in soil and sediment

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17
Q

Redox potential is determined from…

A

the concentration of oxidants and reductant

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18
Q

Oxidants: Oxidation

A

removal of electrons from a compound

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19
Q

Oxidants

A

oxygen, nitrate, nitrite, manganese, iron, sulfate, and CO2

20
Q

Oxidation

A

removal of electrons from a compound

21
Q

Reduction

A

addition of electrons to a compound

22
Q

Reductants

A

various organic substrates and reduce inorganic compounds

23
Q

root exudates

A
  • Chelate and mobilize mineral nutrients

- provide energy for microbes

24
Q

Adaptions in the rhizosphere

A
  • significantly influence nutrient uptake

- crucial to plant adaptation to adverse environmental conditions

25
Q

Organic chelating agents (peptides and sugars)

A
  • extract metal ions from minerals and rocks
  • some metal complexes in the environment are not found in some form of chelate ring (e.g. with a humic acid or a protein)
  • metal chelates are relevant to the mobilization of metals into plants and microorganisms
  • selective chelation of heavy metals is relevant to bioremediation
26
Q

Organic chelating agents (peptides and sugars)

A
  • extract metal ions from minerals and rocks
  • some metal complexes in the environment are not found in some form of chelate ring (e.g. with a humic acid or a protein)
  • metal chelates are relevant to the mobilization of metals into plants and microorganisms
  • selective chelation of heavy metals is relevant to bioremediation (e.g. removal of 137Cs from radioactive waste)
27
Q

Concentration of a specific ion in rhizosphere relative to bulk soil

A

lower
higher
similar

28
Q

Factors affecting ion concentration

A
  • concentration in the bulk soil solution
  • rate of movement of ion to root surface
  • rate of nutrient uptake by the root
29
Q

Nutrient concentration examples

A
  • Ryegrass roots: deplete K concentration in soil solution below 80 micro moles in the rhizosphere enhanced release of (non-exchangeable) K.
  • Canola (rape) depletion of K and Mg associated with a pH decrease in the rhizosphere to 4.0 resulted in release of non-exchangeable K and Mg which introduced irreversible transformations of mica.
  • water uptake is greater than ion uptake: ions accumulate in the rhizosphere
30
Q

Salt accumulation in Rhizosphere:

Low solubility salts such as CaCO3 and CaSO4 accumulation

A
  • may not be harmful to plants in acid soils, but can be a problem in saline soils
  • increasing salts concentration and osmotic potential of the soil solution decreases water availability to plants
31
Q

Rhizosphere pH and bulk soil pH

A

can differ up to two units

32
Q

Rhizosphere pH and Redox potential:

Root induced factors

A
  • imbalance in cation/anion uptake ratio and corresponding differences in net release of H+ and HCO3- or (OH-)
  • Excretion of organic acids (or organic acids produced by increased microbial activity in the rhizosphere)
33
Q

CO2 production by roots and microbes:

Aerated Soils

A
  • CO2 rapidly diffuses from roots and has small effect on rhizosphere pH
  • mainly the CO2 dissolved in the soil solution which affects the rhizosphere through the influence in HCO3- and H+ concentrations
34
Q

Rhizosphere pH change

A
  • pH buffering capacity of soil

- Initial pH of the bulk soil

35
Q

pH buffering capacity of soil

A

influenced by organic matter and clay contents

-residual lime available for reaction

36
Q

Nitrogen source and rhizosphere pH

A
  • N source (NH4+ or NO3-)influences the release by roots of H+ or HCO3- to maintain electrical neutrality
  • Neutral or alkaline soils
  • Acid soils
37
Q

Nitrogen source and rhizosphere pH: neutral or alkaline soils

A

ammonium (through acidification) enhances the solubility of Ca and other ions that are precipitated in the alkaline soil

38
Q

Nitrogen source and rhizosphere pH: neutral or alkaline soils

A

ammonium (through acidification) enhances the solubility of Ca and other ions that are precipitated in the alkaline soil

39
Q

Nitrogen source and rhizosphere pH: acid soils

A
  • ammonium usually does improve nutrient uptake

- Nitrate can increase pH in the rhizosphere and increase P uptake from acid soils

40
Q

Legumes and rhizosphere pH

A
  • N requirements met with N2
  • Nitrate not being taken up so more cations enter roots than anions
  • Net excretion of H+
  • Can influence uptake of other elements due to the acidification in the rhizosphere
41
Q

Nutritional status of plants and rhizosphere pH: Micronutrient deficiencies

A
  • Zn in cotton results in acidification in the rhizosphere
  • Fe deficiency in non-grass plants
  • Net release of H+ acidifies soil to increase solubility of these micronutrients
42
Q

Acidification of rhizosphere also observed in

A

P deficient dicots

43
Q

Micronutrient deficiencies: Net release of H+ acidifies soil to increase solubility of these micronutrients

A
  • acidification is confined to apical root zone

- adaptation to improve growth

44
Q

Redox potential

A
  • redox potential changes associated with water logging and changes in nutrient availability
45
Q

redox potential:
Plants adapted to water-logging main ______ in the rhizosphere by the transport of _____ from the shoot to the roots where it is released into the rhizosphere. It decreases________________________

A

high redox potentials

O2

phytotoxic effects of Mn and Fe

46
Q

Aerated soils

A
  • zones of anaerobic microsites occur even in well aerated soils
  • such sites are more abundant in rhizosphere
  • denitrification occurs under anaerobic conditions (conversions of nitrate to N gas)
  • Compacted soils will have increase in anaerobic microsites
    * Planted soils more likely to be compacted
    * Potentially greater rates of denitrification

Final Soil Fertility (4 decks)

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