A Global Meta-Analysis on Nitrogen Deposition Effects on Dissolved Organic Carbon and Nitrogen Dynamics

Global atmospheric nitrogen (N) deposition have profound effects on terrestrial ecosystems. This study synthesized data from 54 papers and carried out a meta-analysis of experimental N-addition effects on 14 variables related to soil dissolved organic carbon and N (DOC and DON) dynamics. Experimental N deposition generally increased soil DOC (+14.7%) and DON (+40.9%) production, and DOC leaching (+25.6%), but did not change DON leaching, explained by the increase in dissolved organic matter aromaticity (+28.3%), soluble phenolic (+23.5%), microbial activity (e.g. net nitrification: +21.2%, N2 O emission: +69.1%) and NO3 - leaching (+108.7%). N-induced suppression of phenol oxidase and peroxidase activity (-40.0%) led to the increase of phenolic. The response of DON leaching to N deposition was most significantly positive in forests (+80.4%), which was probably attributed to elevated soil total N (TN: +16.6%), followed by grassland (+54.5%; TN: +10.9%) and plantation (+41.7% TN: -1.8%), but the change of DOC leaching from natural forests was insignificant. DON leaching under N deposition significantly increased in subtropical zones (+34.1%), but was not significant in temperate zones, which was in contrary to DOC leaching (temperate zones: +34.6%). Because N-applied methods resulted in different effects on DOC and DON dynamics, canopy N-addition accurately reflecting natural N deposition should be enhanced in the future studies. Long-term experiments with high N deposition rates would not aggravate soil C losses from N deposition, but would stimulate persistent DON leaching although chronic N-addition can inhibit MBN and DON production. The effect sizes of N deposition on soil pH had a significant correlation with DOC dynamics, but little link with DON dynamics. These results are useful for better understanding the responses of DOC and DON dynamics to global N deposition and the underlying mechanisms of N deposition effects on ecosystem C and N cycles as well as its functions