Microbial Activity in the Rhizosphere

The rhizosphere is a very complex environment in which the effects of the plant on soil microorganisms and the effects of the microorganisms on the plant are interacting and are interdependent. Plant root exudates and breakdownproducts attract microbes and feed them and, in turn, the plants often bene?t from the microbes. Interactions among microorg- ismsandplantrootsareessentialfornutritionalrequirementsoftheplant. Plant growth, development and productivity are largely dependent on the soil environment in the root region rhizosphere. The new techniques of studying the rhizosphere enables us to get a much better understanding of the dynamics of the rhizosphere population, such rhizosphere studies beingofinteresttoagriculturists,soilbiologists,chemists,microbiologists andmolecularbiologists. The rhizosphere microbes in?uence the root environment in several ways. They may change the oxidation-reduction potential, in?uence the availabilityofmoistureandnutrients,producegrowthinhibitingorgrowth promoting substances in the form of exudates, provide competition and possiblyinducemanyothereffects.Mycorrhizalassociationsarebene?cial in mineral uptake and in increasing root surface area for effective ion absorption. Antagonism,competitionandsynergisminsoilandtherhizoplane(r- zosphere) are the most important microbial interactions to consider in the study of rhizosphere biology. With the growing information on the production of growth regulators, competitiveness of the microbes in the rhizosphere, microsymbionts, and other factors, their effect upon plant growth will become more evident. Experiments on the introduction of microbes or their products in the rhizosphere will help to improve our understandingofthebiologyoftherhizosphere.

Contenu
Rhizosphere Biology an Overview.- Methods and Techniques for Isolation, Enumeration and Characterization of Rhizosphere Microorganisms.- Root Exudates as Determinant of Rhizospheric Microbial Biodiversity.- Rhizosphere Microbial Community Dynamics.- The Role of Rhizotrons and Minirhizotrons in Evaluating the Dynamics of Rhizoplane-Rhizosphere Microflora.- Significance of Bacteria in the Rhizosphere.- Interactions Among Beneficial Microorganisms.- Bacterial Community Composition and Activity in Rhizosphere of Roots Colonized by Arbuscular Mycorrhizal Fungi.- Mycorrhizosphere Concept.- Molecular Techniques for Understanding the Microbial Community Structure in Mycorrhizosphere.- Arbuscular Mycorrhizal Fungi and the Formand Functioning of the Root System.- Fungal Recognition Responses to Host Derived Signals by Arbuscular Mycorrhizal Fungi.- Interactions Between Ectomycorrhizal Fungi and Rhizospheric Microbes.- Role of Beneficial Microsymbionts on the Plant Performance and Plant Fitness.- Bacteria Helping Mycorrhiza Development.- Rhizosphere Regulation of Preinfection Behavior of Oomycete Plant Pathogens.