ECOLOGICAL IMPLICATIONS OF SPECIFICITY BETWEEN PLANTS AND RHIZOSPHERE MICROORGANISMS

This chapter discusses the ecological implications of specificity between plants and rhizosphere micro-organisms. The importance of specificity during infection or subsequent plant growth on plant competitive ability and subsequent community structure has a great potential influence. The plant population biology and rhizosphere microbiology elucidates the role of rhizosphere micro–organisms and evolved specificity on plant competition, species distribution, and community structure in different environments. This chapter discusses the specificity in relation to the effectiveness of mutualistic plant–micro–organism associations to evolve the fitness of both organisms. The specificity at this level of association is demonstrated between plant species, cultivars, and genotypes and isolates of rhizosphere bacteria or mycorrhizal fungi. Specificity between plants and growth-promoting micro-organisms occurs at either of two stages of these associations: during infection of the root system to form root nodules or mycorrhizas, or during subsequent growth of the infected plant host. The major categories of rhizosphere micro–organisms capable of altering plant growth and the proposed mechanisms of action for plant growth–promoting rhizobacteria are also tabulated. Infection specificity can be demonstrated with root nodule bacteria and less so with mycorrhizal fungi and may result from the specific association of effective plant–microbe combinations. © 1991 Academic Press Limited