Microbiologyprocedure.com Community Toolbar Download Image

Submit Your College, Institute, Company, Products for FREE

Index >> Rhizosphere and Phyllosphere >> Rhizospher Effect

Rhizosphere and the Phyllosphere
Rhizosphere Introduction
Rhizospher Effect
Nitrogen Fixation in the Rhizosphere
Alteration of Rhizosphere Microflora
Associative and Antagonistic Activities in the Rhizosphere
Root Exudates
Organic Compounds Detected in Plant Root Exudates
Fungistasis
Techniques of Rhizosphere
The Soil Dilution and Plate Count Method
The Soil Plate
The Soil Box
The Contact Slide Technique
Artificial Rhizosphere
Model System

Rhizospher Effect

	Rhizosphere Effect Greater rhizosphere effect is seen with bacteria (R : S values ranging from 10 to 20 or sometimes more) than with actinomycetes or fungi. Only negligible changes are noted with regard to protozoa and algae. Literature abounds with reports on quantitative changes in microorganisms in the rhizosphere of crop plants. Qualitative studies, however, reveal some distinct selective influence of the root system. An example of this is the preferential stimulation of Gram-negative non-sporulating rod-shaped bacteria in the root region of many plants.
Several genera of bacteria-Pseudomonas, Arthrobacter, Agrobacterium, Azotobacter, Mycobacterium, Flavobacterium, Cellulomonas, Micrococcus and others have been reported to be either abundant or sparse in the rhizosphere. From the agronomic point of view, the abundance of nitrogen fixing and phosphate solubilizing bacteria in the rhizosphere of crop plants assumes a natural significance. The preponderance of amino acid requiring bacteria in the rhizosphere of crop plants has been consistently observed by many workers.
The preferential stimulation of vitamin requiring bacteria in the rhizosphere has also been emphasized by some workers but the question of the source of B-vitamins in the root region of plants still remains unanswered. Do they accumulate from the activity of microorganisms in soil or are they exuded by the growing root system? Since the quantity of B-vitamins exuded by roots is not as much as that of amino acids, it may be logical to assume that the contribution of microorganisms to the synthesis of B-vitamins in the rhizosphere is higher than that of actively growing root system.
Electron and direct microscopy show that only 4-10 per cent of root surface is colonized by microorganisms in a random fashion depending on the presence of soil organic matter. The proliferation of bacteria takes place at the junction of the epidermal cells indicating that this is an area of maximum root exudation. In this way, root excretions and root derived organic matter provide substrates for microbial proliferation. The microbial ecology in the rhizosphere is also dependent on genotypes-of the plant.

Home | Site map | Submit Article | Directory | Search

Language >> English | Français | Español | Deutsch | Italiano | Portugues | Japanese | Korean | Sim-Chinese