Responses of C:N stoichiometry in plants, soil, and microorganisms to nitrogen addition

Background and aims The deposition of atmospheric N is expected to increase in the future; however, our understanding of the responses of C:N stoichiometry to N deposition in plants, soil, and microorganisms remains elusive. We aim to explore the general patterns and mechanisms of terrestrial C:N stoichiometry to N addition. Methods We present a global meta-analysis based on 827 paired observations from 183 studies to evaluate the responses of above- and belowground C and N concentrations ([C] and [N]) and C:N ratios across various ecosystems to N addition. Using linear mixed-effects models, we tested the effects of N input rates, experimental duration, ecosystem types and background climates on the responses. Results N addition increased [C] in plant shoots and soil, [N] in plant tissues and soil, but decreased microbial biomass [C], and C:N ratios in plant tissues, soil, and microbial biomass. These responses were more pronounced with higher N input rates and longer experimental durations. These N addition effects were similar among cropland, forest, and grassland ecosystems and were independent of background climates. Conclusions Our meta-analysis provided further evidence of the consistent responses of C:N stoichiometry in plants, soil, and microorganisms to N addition. Our results will be useful to modelling the responses of terrestrial C and N cycles to various N deposition scenarios.