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.

Ammonia oxidizing (AOB) and denitrifying bacteria (DNB) play an important role in soil nitrogen transformation in natural and agricultural ecosystems. Effects of long-term fertilization on abundance and community composition of AOB and DNB were studied with targeting ammonia monooxygenase (amoA) and nitrite reductase (nirK) genes using polymerase chain reactiondenaturing gradient gel electrophoresis (PCR-DGGE) and real-time PCR, respectively. A field trial with different fertilization treatments in a rice paddy from Tai Lake region, centre East China was used in this study, including no fertilizer application (NF), balanced chemical fertilizers (CF), combined organic/inorganic fertilizer of balanced chemical fertilizers plus pig manure (CFM), and plus rice straw return (CFS). The abundances and richnesses of amoA and nirK were increased in CF, CFM and CFS compared to NF. Principle component analysis of DGGE profiles showed significant difference in nirK and amoA genes composition between organic amended (CFS and CFM) and the non-organic amended (CF and NF) plots. Number of amoA copies was significantly positively correlated with normalized soil nutrient richness (NSNR) of soil organic carbon (SOC) and total nitrogen (T-N), and that of nirK copies was with NSNR of SOC, T-N plus total phosphorus. Moreover, nitrification potential showed a positive correlation with SOC content, while a significantly lower denitrification potential was found under CFM compared to under CFS. Therefore, SOC accumulation accompanied with soil nutrient richness under long-term balanced and organic/inorganic combined fertilization promoted abundance and diversity of AOB and DNB in the rice paddy.