NO and NO production and functional microbes responding to biochar aging process in an intensified vegetable soil.

Vegetable soils with high nitrogen input are hotspots of nitrous oxide (NO) and nitric oxide (NO), and biochar amended to soil has been documented to effectively decrease NO and NO emissions. However, the aging effects of biochar on soil NO and NO production and the relevant mechanisms are not thoroughly understood. AN tracing microcosm study was conducted to clarify the responses of NO and NO production pathways to the biochar aging process in vegetable soil. The results showed that autotrophic nitrification was the predominant source of NO production. Biochar aging increased the O-containing functional groups while lowering the aromaticity and pore size. Fresh biochar enhanced the AOB-amoA gene abundance and obviously stimulated NO production by 15.5% via autotrophic nitrification and denitrification. In contrast, field-aged biochar markedly weakened autotrophic nitrification and denitrification and thus decreased NO production by 17.0%, as evidenced by the change in AOB-amoA and nosZI gene abundances. However, the amendment with artificially lab-aged biochar had no effect on NO production. With the extension of aging time, biochar application reduced the soil NO production dominated by nitrification. Changes in the NO and NO fluxes were closely associated with soil NH-N and NO-N contents, indicating that autotrophic nitrification played a critical role in NO production. Overall, our study demonstrated that field-aged biochar suppressed NO production via autotrophic nitrification and denitrification by regulating associated functional genes, but not for lab-aged biochar or fresh biochar. These findings improved our insights regarding the implications of biochar aging on NO and NO mitigation in vegetable soils.