In the never-tilled systems, microbial biomass remains high throughout the growing season. Comparisons of extracted lipids from in situ soil microbial communities indicate a high heterogeneity in FAME profiles among samples within each treatment. This heterogeneity most likely results from spatial differences in resources and abiotic conditions. The major difference between years was a higher percentage of branched chain fatty acids recovered in the 1992 than 1993 samples. These fatty acids are common to gram positive bacteria.
Lower recovery suggests a shift in the abundance of bacterial populations between years.
There is however an indication that there is a greater heterogeneity of function within the successional plant community than either the cultivated or never-tilled treatments, as reflected in FAME profiles. FAME and Biolog are effective tools for initially characterizing differences in the dominant members of microbial communities associated with varying agricultural practices. Future studies are planned to identify and then demonstrate which selective pressures associated with changes in agricultural management drive the shifts in microbial populations and energetics.