Microbial community structure in a silty clay loam soil after fumigation with three broad spectrum fungicides.

The short-term effect of three broad spectrum fungicides on microbial activity, microbial biomass, soil ergosterol content, and phospholipid fatty acid (PLFA) profiles was studied. A silty clay loam soil was treated separately with captan, chlorothalonil and carbendazim at three different dosages of each fungicide. Chlorothalonil and carbendazim significantly altered soil microbial activity. However, changes in soil microbial biomass were only observed in soil treated with higher dosages of these fungicides. All dosages of fungicides significantly decreased fungal biomass as estimated by soil ergosterol content. PLFA analysis indicated that there was a shift in PLFA pattern. Higher dosages of all three fungicides decreased a straight-chain PLFA 22:0. In addition, soil treated with carbendazim increased cyclopropyl fatty acids. Compared to untreated soil, higher dosages of both captan and chlorothalonil affected PLFA 10Me 16:0, indicating that these fungicides can reduce actinomycetes population. Finally, our results suggest that application of both captan and chlorothalonil decreased Gram-positive to Gram-negative ratio.