Organic fertilizer amendment regulated the pattern and product characteristics of nitrate reduction processes in arable soils

Organic fertilizers can enhance soil health and multifunctionality in agroecosystems, but their impact on nitrate reduction processes and associated soil-borne greenhouse gas emissions remains insufficiently understood. Our research found that organic fertilizer amendment in upland arable soils enhanced the contribution of fungal denitrification to N₂O emissions, while decreasing N₂O/(N₂O+N₂) ratio, primarily by enhancing fungal-bacterial denitrifier mutualism. This effect on the magnitude and pattern of N₂O and N₂ emissions were also depended on soil nitrate content In paddy soils, biochar application significantly reduced N₂O fluxes and N₂O/(N₂O+N₂) ratios, which was mainly attributed to the changes in the abundance and composition of nitrate reducing microorganisms. Specifically, biochar simultaneously increased denitrification and dissimilatory nitrate reduction to ammonium (DNRA) rates, and shifted more NO₃^– partitioning toward DNRA process. These promoting effects were primarily due to the increased carbon availability and the altered nitrate reducer communities. Collectively, our study suggests that organic fertilizer amendment in arable soils is helpful for alleviating the environmental effect of N fertilizer, which deepens our understanding of how organic fertilization regulates N cycling in the agroecosystem.