Effects of two ergosterol-inhibiting fungicides on soil ergosterol and microbial biomass

Abstract

The effects of two ergosterol biosynthesis-inhibiting fungicides, epoxiconazole and triadimefon (at 2 and 20 ×, and 1 and 10 × field rate, respectively), and of straw amendment on ergosterol and microbial biomass C in a sandy loam soil, were investigated. Initial soil ergosterol and microbial biomass C contents were about 1.6 μg g −1 and 330 μg g −1 soil, respectively. Both concentrations of the fungicides decreased soil ergosterol content by about 30% after 7 days incubation in unamended soil, following which contents were broadly similar to the control soil. Microbial biomass C remained largely unaffected in the unamended soil, except for a temporary inhibition of about 12% caused by triadimefon after 13 days incubation. After amendment of the soil with wheat straw, the inhibition of ergosterol biosynthesis reappeared, ranging from 4 to 34%, with epoxiconazole having a greater effect than triadimefon, both compared to ergosterol biosynthesis in soils given straw without the biocides. This inhibition was also transient, but was longer-lasting than in the unamended soil. A decrease in soil microbial biomass C, ranging from 5 to 12%, also occurred, in contrast to the unamended treatments. This indicates that the fungicides were more active against the newly synthesized microbial biomass than ainst the original population. Soil ergosterol content was a more sensitive measure of pesticide side-effects than microbial biomass C, and could be a useful method in this respect.