Rhizosphere Microbiology

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Rhizosphere Microbiology
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What is Rhizosphere? The region of the soil in
contact with the roots of a plant. It contains
many microorganisms and its composition is
affected by root activities. In another word, it
is an environment under the influence of
plant. The Rhizosphere is the zone surrounding
the roots of plants in which complex relations
exist among the plant, the soil microorganisms
and the soil itself.
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The plant roots and the biofilm associated with
them can profoundly, influence the chemistry of
the soil including pH and the transformation of
mineral compounds.
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Rhizosphere can be divided into Inner
rhizosphere the very root surface Outer
rhizosphere embracing the immediately adjacent
soil
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Rhizosphere effect A stimulation that can be put
on a quantitative basis by the use of the RS
ratio RS ratio number of microorganisms in
the rhizosphere soilnumber of microorganisms in
the non-rhizosphere soil. R/S gt
1, good stimulation R/S 1,
no stimulation R/S lt 1,
inhibition
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Importance of Rhizosphere 1. Plant
health 2. Crop yield 3.
Nutrient cycling
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Methodology Microscopy
Plate count Molecular Biology
technique
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Plant affects the rhizosphere microorganisms
through the release of root exudates What is
root exudate? Small molecules that are released
from plant roots, which include sugars, amino
acids, organic acids and amides.  These molecules
influence soil nutrient availability both
directly and indirectly by stimulating the
activities of certain microbial and fungal
components of the soil biota.
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The exudates contain carbohydrates, organic
acids, vitamins and many other substances
essential for life. From 5 percent to 40 percent
of the total dry matter production of organic
carbon from photosynthesis may be released as
exudates!
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When plants begin to decline, the amount of
organic carbon released as exudates increases.
Mineral deficiencies, low amounts of soil air and
severe wounding are major causes for the
increase. Another way to say this is that an
increase in exudates would be caused by
over-pruning, construction injury, planting too
deeply, over-watering, compaction and planting
plants in soils that have a pH too high or too
low for their optimal growth.
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Factors affecting the amount and the composition
of root exudates
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1. Plant species and developmental stage
2. Variety
3. Temperature
4. Light
5. Plant injury
6. Atmosphere
7. Foliar sprays
8. Plant nutrient
9. Moisture
10. Microbial activity

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Translocation of microorganisms in the
rhizosphere When seeds are used as the carrier
for introducing various bio-pesticide and
bio-fertilizer. It is important to understand
the movement of these agents in the rhizosphere.
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