BIODIVERSITY OF SOIL MICROBIAL COMMUNITIES IN AGRICULTURAL SYSTEMS

The productivity and health of agricultural systems depend greatly upo n the functional processes carried out by soil microorganisms and soil microbial communities. The biodiversity of the soil microbial communi ties and the effect of diversity on the stability of the agricultural system, is unknown. Taxonomic approaches to estimating biodiversity of soil microbial communities are limited by difficulties in defining su itable taxonomic units and the apparent non-culturability of the major ity of the microbial species present in the soil. Analysis of function al diversity may be a more meaningful approach but is also limited by the need to culture organisms. Approaches which do not rely on culturi ng organisms such as fatty acid analysis and 16S/18S rRNA analysis hav e provided an insight into the extent of genetic diversity within comm unities and may be useful in the analysis of community structure. Scal e effects, including successional processes associated with organic ma tter decomposition, local effects associated with abiotic soil factors , and regional effects including the effect of agricultural management practices, on the diversity of microbial communities are considered. Their impact is important in relation to the minimum biodiversity requ ired to maintain system function.