MICROBIAL DYNAMICS IN ARID ECOSYSTEMS - DESERTIFICATION AND THE POTENTIAL ROLE OF MYCORRHIZAS

In semiarid and arid ecosystems, structure and functioning of plant co mmunities is regulated by the timing of moisture inputs and the abioti c factors affecting nitrogen availability. Soils of these regions supp ort a large diversity of belowground microflora and microfauna which h ave a significant role in the functioning and stability of these ecosy stems. Plants that have been studied from these habitats have very oft en been found to be mycorrhizal (89% of 61 plant families surveyed in arid and semi-arid regions world-wide were found to be mycorrhizal). T his paper discusses mycorrhizal-plant interactions and their synergist ic effects on plant growth and nutrient dynamics, and attempts to link changes in aboveground plant community dynamics in desert system to c hanges in the temporal and spatial dynamics of the root zone biota. Fa ctors which directly or indirectly determine the occurrence of mycorrh izal propagules, are potentially important in subsequent plant establi shment and diversity since various mycorrhizal fungi can have differen t physiological effects on their hosts. The successful establishment o f plants and the maintenance of plant diversify may be also determined in the semiarid and arid environment by the presence of preferred/ ap propriate mycorrhizal fungi. Without successful establishment and main tenance of appropriate mycorrhizal fungi, plant species composition an d nutrient dynamics within semiarid and arid ecosystems can be altered , and lead to further degradation of these lands.