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

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.