Variation in Composition and Structure of Soil Microbial Communities in Michigan Old Fields

Goodfriend, W. L. and L. C. Broughton

Presented at the All Scientist Meeting (1998-07-21 to 1998-07-22 )

We surveyed soil microbial communities in several successional old fields in southwestern Michigan to assess “soil” and “plant” effects on community structure. Six replicate early successional plots of the same soil fertility and agronomic history were compared to four late successional fields of different fertility and history. In order to more closely examine soil and plant effects on the microbial community, we sampled under the same plant species, Andropogon gerardii, as well as under the mixed plant community in the four late successional fields. Wecharacterized the soil communities with microbial biomass C, plate counts, N-mineralization rates, patterns of substrate utilization (BIOLOG) and marker fatty acids (PLFA) at peak plant biomass (August) and plant senescence (October). Preliminary results indicate that microbialcommunities in the early successional plots had differing BIOLOG and PLFA patterns than those in the late succession fields, possibly due to differences in soil fertility or agronomic history. In the four late successional fields, maximum potential N mineralization and substrateutilization differed between the communities under A. gerardii and those under the mixed plant community. These differences may be due to direct effects of plant roots or indirect effects of plants on soil moisture or other resources. Results from this study suggest that soil history, and possibly fertility, may drive differences in microbial communities. The difference in microbial functional response to an individual plant species, A. gerardii, also indicates that the composition of the plant community may be important. Further exploration of microbial community structure should include examination of both site history and the overlying plant community.Return to Contents

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