IMPACT OF CARBON AND FLOODING ON THE METABOLIC DIVERSITY OF MICROBIALCOMMUNITIES IN SOILS

The assumption that carbon and soil water content are major determinan ts of microbial community structure and function is rarely questioned because of substantial evidence of the impacts of these variables on s pecific populations and functions. The significance of carbon and wate r for metabolic diversity at the microbial community level was tested on the field scale in agricultural plots varying in carbon inputs and in whether they were flooded. Surface soils in which rice straw was in corporated or burned and which were hooded or unflooded were sampled a t monthly intervals three times during the flooded winter period (Janu ary to March) and again 1 month postdraining. Biomass carbon and nitro gen were not affected by treatments, active bacterial counts showed sl ight increases, and respiration rates were increased by carbon inputs and flooding, Biolog microplates were inoculated with soil extracts to quantify the metabolic diversity of the soil microbial community. Can onical correspondence analysis and the Monte Carlo permutation testing shelved that differences in substrate utilization patterns were signi ficantly related (P < 0.001) to carbon and flooding treatments, Biolog substrates whose metabolism was altered by the treatments were consis tent across dates and tended to be positively related (utilization enh ancement) to carbon inputs and negatively related to winter flooding. The importance of carbon as an environmental variable increased over t ime after straw treatment, whereas the importance of water became evid ent after flooding and decreased after drainage, The effect of long-te rm rice straw incorporation on substrate utilization patterns at anoth er field site was consistent with these results despite the dissimilar ities of the two soils.