Long-term effects of nitrogen deposition on carbon assimilation characteristics in the past three decades in a typical subtropical watershed

Abstract

• Trends of N deposition during the past 30 years at a watershed scale • N deposition effect on terrestrial and aquatic ecosystems at a watershed scale • N deposition effect on C assimilation characteristics at a watershed scale Carbon (C) assimilation is primarily dominated by gross primary production (GPP), which is largely limited by nitrogen (N) availability in terrestrial and aquatic ecosystems. Atmospheric N deposition alters the N availability in terrestrial and aquatic ecosystems and regulates C and water cycling processes, including water use efficiency (WUE). This study evaluated the impacts of N deposition on C assimilation characteristics in the Poyang Lake watershed from the 1990s to the 2010s, using data simulated by the model, observational data from monitoring sites, and results published in scientific literature. Results showed an increase in total N deposition flux but a decrease in wet deposition N flux as well as the ratio of reduced oxidized species (NH x /NO y ) in wet deposition in the Poyang Lake watershed over the past three decades. Moreover, the C assimilation potential of forests was higher than other ecosystem types, while N deposition had the greatest overall impact on forest C assimilation. Results also revealed that N deposition played a positive role in sequestering terrestrial and aquatic ecosystem C in this watershed. Findings from this study will expand both our overall understanding and the predictive capacity of C assimilation characteristics under prospective increases in N deposition while also providing an important reference for afforestation, water resources management, and climate change mitigation decision-making policies in subtropical watersheds globally.