Distinct Denitrifying Phenotypes of Predominant Bacteria Modulate Nitrous Oxide Metabolism in Two Typical Cropland Soils.

Denitrifying nitrous oxide (NO) emissions in agroecosystems result from variations in microbial composition and soil properties. However, the microbial mechanisms of differential NO emissions in agricultural soils are less understood. In this study, microcosm experiments using two main types of Chinese cropland soil were conducted with different supplements of nitrate and glucose to simulate the varying nitrogen and carbon conditions. The results show that NO accumulation in black soil (BF) was significantly higher than that in fluvo-aquic soil (FF) independent of nitrogen and carbon. The abundance of most denitrifying genes was significantly higher in FF, but the ratios of genes responsible for NO production (nirS and nirK) to the gene responsible for NO reduction (nosZ) did not significantly differ between the two soils. However, the soils showed obvious discrepancies in denitrifying bacterial communities, with a higher abundance of NO-generating bacteria in BF and a higher abundance of NO-reducing bacteria in FF. High accumulation of NO was verified by the bacterial isolates of Rhodanobacter predominated in BF due to a lack of NO reduction capacity. The dominance of Castellaniella and others in FF led to a rapid reduction in NO and thus less NO accumulation, as demonstrated when the corresponding isolate was inoculated into the studied soils. Therefore, the different phenotypes of NO metabolism of the distinct denitrifiers predominantly colonized the two soils, causing differing NO accumulation. This knowledge would help to develop a strategy for mitigating NO emissions in agricultural soils by regulating the phenotypes of NO metabolism.