Effects of metam sodium fumigation on soil microbial activity and community structure

Metam sodium (MS) is a widely used soil fumigant with broad biocidal activity. The impact of MS on soil microbial community structure and function is largely unknown. We investigated the effects of fumigation with field- relevant doses of MS in soil microcosms using traditional heterotrophic activity measures (C and N mineralization), a substrate-utilization assay, and fatty acid analysis. Our results suggest that fumigation with MS results in persistent changes (at least 18 wk) in heterotrophic activity and fatty acid composition of the microbial biomass. Lack of recovery of heterotrophic activity and changes in fatty acid composition after fumigation suggest that MS has the potential to alter important microbially mediated functions such as nutrient cycling and pollutant degradation. Preliminary fatty acid data suggest that actinomycetes and other gram-positive organisms may recover preferentially after fumigation with MS. Although community fatty acid analysis shows promise as a screening tool in soil microbial toxicity studies, more detailed information can be obtained from analysis of phospholipid fatty acid (PLFA) and other specific lipid fractions.