Differential responses of soil N2O to biochar depend on the predominant microbial pathway

Biochar amendment has been proposed as a potential strategy to reduce soil nitrous oxide (N2O) emissions, although experimental studies have generated inconsistent results on N2O emissions following biochar amendment. Differential responses of soil N2O to biochar amendment may depend on soil microbial functional genes abundance and abiotic properties. Here we sampled three types of soil from fields under long-term cultivation of green tea (TG), film greenhouse vegetable cabbage (GV) and Jerusalem artichoke (JA), respectively. We conducted a microcosm experiment to examine N2O emissions from the different soils following biochar amendment. Results showed that biochar amendment increased N2O emissions from the GV soil while decreasing N2O emissions from the TG and JA soils in the presence of nitrogen fertilizer. Biochar amendment increased soil pH and C/N ratio across the three soils. Quantitative PCR (qPCR) analysis showed that biochar amendment also consistently increased the abundances of AOB and nosZ genes but decreased the AOA abundances for all the soils, while the effects of biochar on the abundances of nirK and nirS genes differed between the soils. Our results suggest that biochar amendment can affect the processes of both ammonia oxidation and reduction of N2O to N-2 for all the soils and the net effect of biochar on N2O emissions depended on the predominant process in a specific soil. Biochar-induced increase in N2O emissions in the GV soil was largely attributed to the stimulated nitrification rate, which was primarily driven by AOB. Biochar-induced decreases in N2O emissions in the TG and JA soils were linked to the increased nosZ gene abundances. Overall, the effectiveness of biochar for mitigating N2O emissions is linked to its dominant N2O production pathway in soils.