Straw amendment to paddy soil stimulates denitrification but biochar amendment promotes anaerobic ammonia oxidation

Purpose Organic matter amendment is usually used to improve soil physicochemical properties and to sequester carbon for counteracting climate change. There is no doubt that such amendment will change microbial activity and soil nitrogen transformation processes. However, the effects of straw and biochar amendment on anammox and denitrification activity and on community structure in paddy soil are unclear. Materials and methods We conducted a 30-day pot experiment using rice straw and rice straw biochar to deepen our understanding about the activity, microbial abundance, and community structure associated with soil nitrogen cycling during rice growth. Results and discussion Regarding activity, anammox contributed 3.1–8.1% of N 2 production and denitrification contributed 91.9–96.9% of N 2 production; straw amendment resulted in the highest denitrification rate (38.9 nmol N g −1 h −1 ), while biochar amendment resulted in the highest anammox rate (1.60 nmol N g −1 h −1 ). Both straw and biochar amendments significantly increased the hzsB and nosZ gene abundance ( p