Underappreciated role of canopy nitrogen deposition for forest productivity

• 成果类型: Article
• 署名作者: Li, Xiaowei; Zhang, Chenlu; Zhang, Beibei; Jiang, Li; Tang, Shengqi; Sun, Chenhui; Bai, Yulong; Wang, Yubang; Shi, Yifei; Ma, Lei; Zhang, Wei; Ye, Qing; Yan, Junhua; Wang, Keya; Fu, Juemin; Du, Wenzhi; Ha, Denglong; Ju, Yuxi; Wan, Shiqiang; Hong, Liang; Fang, Yunting; Siemann, Evan; Luo, Yiqi; Reich, Peter B.; Ort, Donald
• 署名单位: Henan University; Henan University; Henan University; Henan University; Chinese Academy of Agricultural Sciences; Institute of Cotton Research, CAAS; Chinese Academy of Sciences; South China Botanical Garden, CAS; Hebei University; Xinyang Normal University; Chinese Academy of Sciences; Shenyang Institute of Applied Ecology, CAS; Rice University; Cornell University; University of Minnesota System; University of Minnesota Twin Cities; University of Michigan System; University of Michigan; University of Michigan System; University of Michigan
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-12870
• DOI: 10.1073/pnas.2508925122
• 发表日期: 2025-08-26
• 关键词: carbon sequestration; terrestrial ecosystems; recent trends; tree growth; limitation; temperate; fertilization; disturbances; responses; climate

摘要

Atmospheric nitrogen (N) deposition is generally expected to stimulate plant carbon (C) sequestration and promote tree growth, thereby mitigating atmospheric CO2 accumulation. Yet, the magnitude of N deposition contribution to forest productivity remains contentious. While correlative studies suggest substantial plant growth enhancement, controlled fertilization experiments typically demonstrate a limited impact. This discrepancy may arise from whether or not to consider canopy N uptake processes. Here, we conducted a 10-y field experiment comparing canopy addition of N (CAN) with understory addition of N (UAN) at the rate of 0, 25, and 50 kg N ha(-1) y(-1) in a temperate deciduous forest in central China. We show that CAN significantly enhanced net primary productivity by 37.0% over control, driven by enhanced leaf litterfall, wood and fine root production, whereas UAN effects were marginal (8%). N-15 isotopic tracing revealed that CAN, through enhanced plant N uptake and increased ecosystem N retention, yielded a 3.5-fold higher C sequestration efficiency (triangle C/triangle N) of 54.5 +/- 7.7 kg C kg(-1) N, than UAN (12.2 +/- 3.4 kg C kg(-1) N) resulted from greater N loss through leaching. Physiological measurements indicated CAN enhanced leaf photosynthetic rates, modified leaf morphology, and extended leaf lifespan via delayed senescence. These findings provide robust empirical evidence that canopy N uptake is crucial for maximizing N-induced forest productivity, thereby holding significant implications for refining global C models and urging modelers to incorporate canopy processes for more accurate projections of future C sinks and climate change mitigation strategies.