Biochar amendments and climate warming affected nitrification associated NO and NO production in a vegetable field.

Soil nitrification driven by ammonia-oxidizing microorganisms is the most important source of nitrous oxide (NO) and nitric oxide (NO). Biochar amendment has been proposed as the most promising measure for combating climate warming; both have the potential to regulate the soil nitrification process. However, the comprehensive impacts of different aged biochars and warming combinations on soil nitrification-related NO and NO production are not well understood. Here, 1-octyne and acetylene were used to investigate the relative contributions of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to potential nitrification-mediated NO and NO production from the fertilized vegetable soil with different aged biochar amendments and soil temperatures in microcosm incubations. Results demonstrated that AOB dominated nitrification-related NO and NO production across biochar additions and climate warming. Biochar amendment did not significantly influence the relative contribution of AOB and AOA to NO and NO production. Field-aged biochar markedly reduced NO and NO production via inhibiting AOB-amoA gene abundance and AOB-dependent NO yield while fresh- and lab-aged biochar produced negligible effects on AOB-dependent NO yield. Climate warming significantly increased NO production and AOB-dependent NO yield but less so on NO production. Notably, the relative contribution of AOB to NO production was enhanced by climate warming, whereas AOB-derived NO showed the opposite tendency. Overall, the results revealed that field-aged biochar contributed to mitigating warming-induced increases in NO and NO production via inhibiting AOB-amoA gene abundance and AOB-dependent NO yield. Our findings provided guidance for mitigating nitrogen oxide emissions in intensively managed vegetable production under the context of biochar amendments and climate warming.