Response of microbial community to a new fungicide fluopyram in the silty-loam agricultural soil

• The impacts of fluopyram on the soil microbes were studied.
• Fluopyram reduced the soil microbial biomass.
• Fluopyram enhanced the microbial respiration activity and microbial community stress.
• Fluopyram altered the soil microbial community structure and function.
• The effect of fluopyram at recommended field rate on the soil microbes was minor.

The impacts of fluopyram on a soil microbial community were studied at three application rates: at the recommended field rate (T1, 0.5 mg/kg soil), three-fold recommended field rate (T3, 1.5 mg/kg soil) and ten-fold recommended field rate (T10, 5 mg/kg soil). Soil samples were taken after 7, 15, 30, 45, 60 and 90 days of application to determine the fluopyram residue and microbial properties (i.e., basal respiration, substrate-induced respiration, microbial biomass carbon, microbial community function and structure). The half-lives of the fluopyram at levels of 0.5, 1.5 and 5 mg/kg in soil were calculated to be 64.2, 81.5 and 93.6 days, respectively. The results demonstrated that fluopyram treatment (T1, T3 and T10) decreased microbial biomass C but increased the basal respiration, substrate-induced respiration, and ecophysiological indices (qCO2). Average well color development (AWCD) represents the oxidative capacity of soil microorganisms cultivated in the BIOLOG micro-plates and usually indicates the overall microbial metabolic capacity. The BIOLOG results revealed that the AWCD in the soil treated with 1.5 and 5 mg/kg fluopyram (T3 and T10) was significantly lower than that of the control during the incubation period. A similar variation in the diversity indices (Simpson index and McIntosh index) was observed. Phospholipid fatty acid (PLFA) analysis revealed that the addition of fluopyram decreased the total amount of PLFAs, bacterial biomass (both Gram-positive (GP) bacteria and Gram-negative (GN)), fungal biomass, the ratios of the GN/GP and fungi/bacteria at all incubation times. Principal component analyses (PCA) suggested that the addition of fluopyram shifted the soil microbial community structure and function. Hence, fluopyram has a harmful effect on overall soil microbial activity, and changed soil microbial community structure and function.