The Effects of N Addition on Soil Microbial Residues in Croplands and Forests: A Meta-analysis

Nitrogen (N) availability in soil regulates microbial communities and then affects the decomposition and formation of microbial residues carbon (C), which have great impacts on soil organic carbon (SOC) sequestration. However, Asia has not yet well-assessed patterns and determinants of microbial residues C in response to N input. Here, we performed a large-scale, systematic meta-analysis of the effects of N addition on microbial residues across cropland and forest ecosystems. A total of 31 publications regarding microbial residues were included in our database, with 235 observations. In croplands N addition significantly increased microbial residue and biomass, and total microbial residue contribution to SOC. The responses to N addition of microbial residues and biomass increased with N addition rate (0-800 kg N ha(-1) year(-1)) and there was a bidirectional positive effect between these two. In forest ecosystems, bacterial residues increased by 14.7% in N addition rates of 0-50 kg N ha(-1) year(-1). Moreover, the negative correlation between the duration of N addition and microbial residues is highly significant, indicating that long-term N deposition could threaten SOC transformation and sequestration in forests. These results suggest that N addition effects on microbial residues are ecosystem-specific. This is related to the different main controlling factors affecting the microbial residues in cropland and forest ecosystems under N addition.