Nitrogen deposition favors later leaf senescence in woody species

Abstract

China has experienced an unprecedented increase in nitrogen deposition over recent decades, threatening ecosystem structure, functioning, and resilience. However, the impact of elevated nitrogen deposition on the date of foliar senescence remains widely unexplored. Using 22,780 in situ observations and long-term satellite-based date of foliar senescence measures for woody species across China, we find that increased nitrogen deposition generally delays date of foliar senescence, with strong causal evidence observed at site-to-region scales. Changes in climate conditions and nitrogen deposition levels jointly controlled the direction of date of foliar senescence trends (advance or delay). The spatial variability of nitrogen deposition effects can be related to plant traits (e.g., nitrogen resorption and use efficiencies), climatic conditions, and soil properties. Moreover, elevated nitrogen deposition delays date of foliar senescence by promoting foliar expansion and enhancing plant productivity during the growing season, while its influence on evapotranspiration may either accelerate or delay date of foliar senescence depending on local water availability. This study highlights the critical role of nitrogen deposition in regulating date of foliar senescence trends, revealing a key uncertainty in modeling date of foliar senescence driven solely by climate change and its far-reaching implications for ecosystem-climate feedbacks.