Rhizosphere in soil

1. RHIZOSPHERE
Presented by:
Narpat Singh
Msc. 3rd sem

2. 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 was defined by Lorents Hiltner as “the
soil compartment influenced by the roots of growing
plants.”
 “Root zone.”A very narrow zone (a few mm) around the
root. Contains root exudates and microbes. Rhizosphere
is a relatively stable, nutrient-rich environment.

3.  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.
 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.

4.  Rhizosphere can be divided into：
 Inner rhizosphere: the very root surface
 Outer rhizosphere: embracing the immediately
adjacent soil

5. RHIZODEPOSITION
 Release of organics form roots.
5-20% roots exucants
 Rhizodeposition describes that total
carbon transfer form root to soil.
 Plants roots secrete various
nutrients rich compund into the
surrounding soils,this process
called Rhizodeposition.
 Rhizodeposition can amount up to
25% of newly fixed
photosynthates.

6.  This nutritional enrichment around roots creats unique
environment for soil microorganism including the
rhizosphere (that’s volume of soil around roots influenced
by roots exudation) and the rhizoplane (the immediate
root epidermal surface that interfaces that rhizosphere
soil.
 It includes releases come form secretion , exudates ,
lysates , mucilage and mucigel.
 The term rhizodeposition includes (Root exucates ,
mucilage , death & decay part of root).
 Mucilage:- Root mucilage form a gelatinous layer
surrounding the root tip and is one of the few clearly
visible signs of organic carbon excretion from roots. Its
mainly composed of polysaccharides of 106-108 Da in
size and its actively secreted by exocytosis from root cap
cells. Alongside polysaccharides , its also contains
proteins and some phospholipid.

7.  Exudates:- exudates are defined as diffusible
compound which are lost passively by the root and
over which the root extract little control. The
dominants organic compounds in roots reflect those
compound central to cell metabolism and include
free sugers , aminoacid and organic acid
 Lysate:- compound released of death and lysis of
root cells

8. RHIZOSPHERE EFFECT
 Compared to non-rooted bulk soil , the rhizospheric
soil around the plant root contains much larger
population of microorganism.
 A stimulation that can be put on a quantitative basis
by the use of the R：S ratio
 R：S ratio = number of microorganisms in the
rhizosphere soil：number of microorganisms in the
non-rhizosphere soil.
 R/S > 1, good stimulation
 R/S = 1, no stimulation
 R/S < 1, inhibition

9.  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.

10. ORGANIC COMPOUND RELEASED BY
PLANT ROOT
Sugars and Polysaccharides.
Amino Acids.
Organic Acids.
Fatty Acids.
Sterols.
Growth factors.
Enzymes.
Flavonones and Nucleotides.