Restoring farmland to forest increases phosphorus limitation based on microbial and soil C:N:P stoichiometry-a synthesis across China

Soil and microbial biomass C:N:P ecological stoichiometry can indicate element balance and energy flow, which plays a vital role in the terrestrial biogeochemical cycle. However, comprehensive understanding is still lack on the belowground stoichiometric balance and the related factors in large-scale returning farmland to forest lands. Here, a meta-analysis with 2469 pair observations was used to explore the responses of soil and microbial biomass ecological stoichiometry to large-scale returning farmland to forest in China. We found that returning farmland to forest significantly enhanced the overall response ratios of soil C:N (20.25%), N:P (25.48%), C:P (61.54%), microbial biomass C:P (98.50%) and N:P (34.26%). The response ratios of soil C:N, N:P and C:P rose with the increase of restoration age, and decreased with the increase of soil depth. The response ratios of soil and microbial biomass N:P and C:P in mixed forests were higher than those in coniferous forests and broad-leaved forests. Clay content, restoration age and forest type were important factors affecting the response ratios of soil C:N, N:P and C:P, while clay content and mean annual precipitation significantly affected the response ratio of microbial biomass C:P. Our findings suggest that returning farmland to forest changes belowground stoichiometric balance and shows a P limitation trend.