Microbial effects of prolonged nitrogen fertilization and straw mulching on soil N2O emissions using metagenomic sequencing

Abstract

Nitrous oxide (N₂O) emissions from agricultural soils significantly contribute to climate change. While straw mulching and nitrogen fertilization are crucial agricultural practices influencing soil nitrogen dynamics, their long-term effects on N₂O emissions and the underlying microbial mechanisms remain elusive. The main objectives of this study were to investigate the long-term effects of straw mulching and nitrogen fertilization on soil N₂O emissions, microbial communities, and nitrogen cycling functional genes in a winter wheat-summer maize rotation system in the Guanzhong Plain, China. This study investigated the microbial-driven effects of straw mulching at rates of 0 and 4500 kg ha⁻¹ (namely CT and SM, respectively) and nitrogen application at rates of 0, 240 kg N ha⁻¹ (namely N0 and N240, respectively) on N₂O emissions in a field experiment established in 2003. Nitrogen fertilization significantly increased N₂O emissions, nitrification and denitrification potentials, while straw mulching had no significant effect. Compared to CTN0 and SMN0 treatments, cumulative soil N₂O emissions under CTN240 and SMN240 increased by 317.4 % and 238.5 %, soil nitrification potential (NP) increased by 262.1 % and 117.3 %, and soil denitrification potential (DNP) increased by 92.91 % and 52.53 %, respectively. Nitrogen fertilizer application increased the abundance of nitrification and denitrification genes, thereby stimulating N₂O emissions. However, straw mulching promoted the abundances of assimilatory nitrate reduction (ANRA), dissimilatory nitrate reduction (DNRA), and nosZ genes, facilitating the reduction of N₂O reduction to N₂ in the absence of nitrogen fertilization. Partial least squares path modeling (PLS-PM) revealed denitrification functional genes directly influenced N₂O emissions, while soil properties and microbial communities indirectly contributed to increased emissions. Among these factors, soil NH₄⁺-N and DNP were the primary drivers of N₂O emissions. These findings highlight the importance of integrated nitrogen management and straw mulching strategies for mitigating N₂O emissions from agricultural ecosystems.