Global patterns of the interactive effects of N and P enrichment on terrestrial microbial biomass

Nitrogen (N) and phosphorus (P) are key components in biogeochemical cycling and considerable efforts have been made to understand the effects of their availability on microbial biomass. Nevertheless, the interplay between N and P supply in modulating soil microbes remains unclear. We conducted a comprehensive global analysis of 108 studies spanning boreal to tropical regions to evaluate their interactive impacts on microbial biomass. The findings revealed a significant decrease in microbial biomass with N addition, whereas P supplementation resulted in a notable increase in microbial biomass. Among the observed interactive effects, additive effects were predominant. More importantly, we found that among all of the assessed factors, the impacts of N-P interaction on soil microorganisms are dependent on changes in soil pH. In conclusion, our findings provide valuable insights into the interactive effects of N and P enrichment on microbial biomass. These findings will contribute to the development of global models that predict the impacts of N and P enrichment on soil microbes and ecosystem functions.