Impact of nitrogen and phosphorus amendments on nitrogen‐cycling microbial abundances and potentials: A meta‐analysis

Abstract The rapid increase in nitrogen (N) and phosphorus (P) availabilities in terrestrial ecosystems has led to sustained shifts in soil microbial communities and microbially‐mediated N‐cycling. However, the specific effects of N and P amendments on N‐cycling microbes are poorly understood. This meta‐analysis synthesizes the effects of N and/or P amendments on the abundances and functional potentials of N‐cycling genes involved in N₂ fixation, organic N mineralization, nitrification, and denitrification across natural ecosystems and diverse soil conditions in China. Our findings indicate that ammonia‐oxidizing bacteria (AOB) showed greater responsiveness to N amendment than ammonia‐oxidizing archaea (AOA), and AOB amoA abundance increased while AOA amoA abundance decreased with P amendments. Additionally, the abundance of nirS declined, while nirK abundance remained unresponsive to both N and P amendments. These findings highlight the distinct ecological niches occupied by microbial groups with equivalent functions in response to N and P amendments. Moreover, our findings indicate that soil N and P availabilities, along with soil acidification induced by N additions and microbial biomass carbon content, are key factors regulating N‐cycling gene abundances and potentials. The driving mechanisms for N‐cycling genes and their corresponding potentials appear to be distinct, with gene abundance showing only a limited influence on functional potentials. This suggests that factors such as soil properties and microbial community compositions may be more critical determinants of N‐cycling processes than functional gene abundances with regard to scenarios of increasing N and P deposition.