Greater promotion of DNRA rates and nrfA gene transcriptional activity by straw incorporation in alkaline than in acidic paddy soils

Dissimilarity nitrate reduction to ammonium (DNRA) is of significance in agriculture ecosystems as the process is beneficial to N retention in soils. However, how fertilization regimes influence DNRA rates and functional microbes in agriculture was rarely estimated. In the present study, a 2-year pot experiment was conducted in two contrasting paddy soils to evaluate the effects of straw and nitrogen addition on DNRA process and the related functional microbes, using stable isotope tracer and molecular ecology techniques. The results showed that the abundance and transcription activity of nitrite reductase encoding gene (nrfA) involved in DNRA process and DNRA rates were significantly higher in alkaline soils than in acidic soils. Straw incorporation significantly enhanced nrfA gene abundance and transcription activity, with a greater effect in alkaline soil than in acidic soil. The rates of DNRA, abundance and transcription activity of nrfA gene positively correlated to soil C/N and C/NO 3 − induced by straw application. Sequencing analysis based on nrfA gene transcript showed that Deltaproteobacteria was the most dominant group in both soil types (30.9%–67.4%), while Gammaproteobacteria, Chloroflexi, Actinobacteria were selectively enriched by straw incorporation. These results demonstrated that DNRA activity can be improved by straw return practice in paddy soils while the effect will vary among soil types due to differentiated functional microbial communities and edaphic properties.