IMPACTS OF CARBON AND FLOODING ON SOIL MICROBIAL COMMUNITIES - PHOSPHOLIPID FATTY-ACID PROFILES AND SUBSTRATE UTILIZATION PATTERNS

Phospholipid fatty acid (PLFA) profiles provide a robust measure that can be used to fingerprint the structure of soil microbial communities , and measure their biomass. A replicated field trial, with gradients in substrate and O-2 availability created by straw incorporation and f looding was used to test the ability of PLFA to discriminate soil micr obial communities in different management regimes. Another objective w as to test the usefulness, on a large scale, of some of the proposed i nterpretations of PLFA biomarkers. Using a direct gradient statistical analysis method, PLFA profiles were found to be very sensitive to flo oding and straw treatments. Relative abundances of monounsaturated fat ty acids were reduced with flooding and increased with added carbon, c onsistent with their proposed interpretations as indicators of aerobic conditions and high substrate availability. The cyclopropyl fatty aci ds were not useful as taxonomic indicators of respiratory type, althou gh their responses were consistent with their proposed use as growth c ondition indicators. Branched fatty acids decreased, as a group, in re sponse to high substrate conditions. A specific biomarker for Type II methanotrophs was not found in this rice soil, even under high carbon, low O-2 conditions, which resulted in methane exposure in the soil. D irect comparison of PLFA and substrate utilization patterns indicated that Biolog patterns are highly selective, and do not reflect composit ional changes in soil communities.