Impact of fluxapyroxad on the microbial community structure and functional diversity in the silty-loam soil

The aim of this work was to assess the effect of applying three different doses of fluxapyroxad on microbial activity, community structure and functional diversity as measured by respiration, microbial biomass C, phospholipid fatty acid (PLFA) and community-level physiological profiles (CLPPs). Our results demonstrated that substrate-induced respiration (on day 15) and microbial biomass C (on days 7 and 15) were inhibited by fluxapyroxad, but stimulation was observed thereafter. In contrast, fluxapyroxad addition increased the basal respiration and metabolic quotients (qCO2) and respiratory quotients (QR). Analysis of the PLFA profiles revealed that the total and bacterial biomass (both Gram-positive bacteria (GP) and Gram-negative bacteria (GN)) were decreased within the initial 15 days, whereas those as well as the GN/GP ratio were increased at days 30 and 60. Fluxapyroxad input decreased the fungi biomass but increased the bacteria/fungi ratio at all incubation time. Moreover, high fluxapyroxad input (75 mg fluxapyroxad kg−1 soil dry weight) increased the microbial stress level. A principal component analysis (PCA) of the PLFAs revealed that fluxapyroxad treatment significantly shifted the microbial community structure, but all of the observed effects were transient. Biolog results showed that average well color development (AWCD) and functional diversity index (H') were increased only on day 60. In addition, the dissipation of fluxapyroxad was slow in soil, and the degradation half-lives varied from 158 to 385 days depending on the concentration tested.