Responses of N2O Production and Abundances of Associated Microorganisms to Soil Profiles and Water Regime in Two Paddy Soils

Abstract

Soil moisture is one of the critical factors affecting N2O emissions. The water regime affects the physical and chemical properties of paddy soil in different soil layers, which, in turn, affects N2O emissions and microbial growth. However, there are few reports on the effects of different soil layers and soil moisture conditions on N2O emission characteristics and microbial mechanisms. A 21-day microcosm experiment was performed to research the effects of soil moisture levels (60%, 100%, and 200% water holding capacity, WHC) and different soil layers (0–10, 10–20, and 20–40 cm) on N2O emissions in hydromorphic and gleyed paddy soils. Function microbes involved in nitrification and denitrification were determined by quantitative PCR. Moreover, the abiotic variables pH, Eh, and exchangeable Fe2+, Fe3+, NH4+-N, and NO3−-N were also analyzed. Results showed that N2O emissions of gleyed paddy soil were significantly higher than that of hydromorphic paddy soil, which was consistent with the result of the abundance of nitrifier and denitrifier in the two paddy soils. Soil depth, water content, and their interaction significantly affected N2O emission (p < 0.05). Cumulative emissions of N2O from each layer of the two paddy soils at 100% and 200% WHC were significantly higher than that under 60% WHC (p < 0.05). N2O emissions decreased significantly with the increase of soil depth (p < 0.05), which was consistent with the change in the abundance of soil nitrifier (AOB and AOA) and denitrifier (nirK and nosZ) function genes with soil depth. The abundance of AOB, AOA, and nirK and nosZ genes decreased significantly with soil depth (p < 0.05), but did not respond significantly to the water regime. Based on the results of redundancy analysis, the contents of Fe2+ and Fe3+ were positively correlated with N2O emissions and the abundance of AOB, AOA, and nirK and nosZ genes. These results indicate that N2O emissions and the abundance of associated microbes are selectively affected by soil moisture and soil layers in the two paddy soils.