Globally nitrogen deposition decreased net carbon sequestration in terrestrial ecosystems by increasing plant-derived carbon decomposition rather than soil priming effects: A meta-analysis

Abstract Aims Plant carbon (C) input and soil priming effects (PEs) together determine the net C sequestration of terrestrial ecosystems. These processes are recognized to be largely influenced by nitrogen (N) availability, the global patterns of N deposition effects on soil net C sequestration and the controlling factors for such effects remain unclear. Methods In this study, we conducted a meta-analysis of 2205 observations from 56 studies worldwide to explore the effect of mineral N addition on net C sequestration and the associated drivers. Results The meta-analysis found that although mineral N addition reduced soil PEs, it still decreased soil net C sequestration by increasing plant-derived C decomposition. The decrease of net C sequestration was much greater by urea addition than by ammoniacal and nitrate N addition. In addition, mineral N addition only decreased net C sequestration under pyrolytic C and residue C substrate forms. The higher soil organic C (SOC) and total N (TN) content increased net C sequestration by decreasing soil PEs rather than plant-derived C decomposition. Higher soil clay content reduced net C sequestration by increasing plant-derived C decomposition rather than soil PE. Higher incubation temperature reduced net C sequestration by increasing SOC and plant-derived C decomposition. Longer incubation time increased net C sequestration by reducing the decomposition of SOC and plant-derived C decomposition. Conclusions These results are beneficial for understanding the response of soil net C sequestration to global N deposition, and could improve the prediction of terrestrial ecosystems C balance under global climate changes.