Straw return facilitates the availability of soil nitrogen by altering the metabolic distribution and nitrogen cycling processes

Straw return (SR) has been extensively utilized to enhance soil organic carbon (SOC) levels and soil fertility in agroecosystems. However, the impact of SR on soil nitrogen (N) dynamics, microbial communities, metabolic processes, and the underlying mechanisms remains largely unexplored. Through a multi-year manipulation of SR under continuous corn cropping (CC) and fallow (FR), we demonstrate that SR promotes N availability by altering soil microbial metabolism. Moreover, SR facilitated N turnover by enhancing metabolic pathways, including arginine biosynthesis, alanine, aspartate, and glutamate metabolism, as well as glycine, serine, and threonine metabolism, and pyrimidine and purine metabolism. Additionally, SR resulted in a significant increase in the abundance of microorganisms and functional genes involved in mineralization ( glsA and ureC ), N fixation ( Bradyrhizobium , Altererythrobacter ), dissimilatory nitrate reduction to ammonium (DNRA, Sorangium , napC , and nirB ), and assimilatory nitrate reduction to ammonium (ANRA, nasA ). However, despite a reduction in the relative abundance of nitrification microbes and functional genes (e.g., Nitrososphaerag , Nitrospira , Sphingomonas , amoAB , nxrA ), SR enhanced the content of extractable inorganic N and organic N in the soil. Therefore, SR represents an effective strategy to promote N dynamics and accelerate the restoration of soil fertility. Our results demonstrated that SR alters N cycling processes by modifying microbial community structure and metabolite distribution, thereby increasing soil N availability. • SR promotes straw decomposition by increasing the abundance of r-strategists. • SR enhances the soil organic N pool by mainly increasing AAN. • SR alters the form of microbial N uptake by changing AA to carbohydrates ratio. • SR enhances soil N immobilization by enhancing DNRA, ANRA, and N fixation. • SR does not increase N 2 O emissions.