Soil priming effect and its response to nitrogen addition in regional and global forests: Patterns and controls

Although the priming effect (PE) of soil organic matter mineralization and its response to nitrogen (N) amendment are widely studied in terrestrial ecosystems, great uncertainties in their geographic patterns constrain the establishment of advanced climate-carbon (C) model. By combining a laboratory experiment incubating soils from nine temperate forests in China with a meta-analysis of 32 publications across global forests, we tested the PEs and their response to N addition to explore their geographic patterns and the potential determinants. We found a weak dependence of the PE on latitude and mean annual temperature (MAT) in temperate forests in China, but a significant dependence of the PE on MAT across global forests after controlling for the exogenous C quantity. Soil pH was evidenced to control the geographic patterns of the PE. Consistent with meta-analysis, a general inhibition impact of mineral N addition on PE was detected in the laboratory experiment, ranging from −5.50 to 228.41%. In contrast with an inapparent dependence on MAT at the global scale, N inhibition effect in incubation experiment was experimentally detected to negatively correlate with MAT. Increase in soil N availability basically attenuated the response of PE to N addition. Across the globe, the PE and N inhibition effect in coniferous forests were more sensitive to latitude than those in broadleaved forests. Overall, our results uncovered distinct patterns but consistent controls of PE and N inhibition effect between the regional and global scales, and emphasized the importance of considering forest type in predicting soil C dynamics in response to global change.