Underappreciated role of canopy nitrogen deposition for forest productivity
Abstract
Atmospheric nitrogen (N) deposition is generally expected to stimulate plant carbon (C) sequestration and promote tree growth, thereby mitigating atmospheric CO 2 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%). 15 N isotopic tracing revealed that CAN, through enhanced plant N uptake and increased ecosystem N retention, yielded a 3.5-fold higher C sequestration efficiency (∆C/∆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.
Article Details
Journal Info
Proceedings of the National Academy of Sciences
National Academy of Sciences
Authors (25)
Xiaowei Li
College of Chemistry, Institute of Nuclear Science and Technology, Key Laboratory of Radiation Physics and Technology of Ministry of Education
Chenlu Zhang
Beibei Zhang
State Key Laboratory of Coordination Chemistry, Chemistry and Biomedicine Innovation Center (ChemBIC)
Li Jiang
Department of Radiation Oncology The First Affiliated Hospital of Guangxi Medical University Nanning China
Shengqi Tang
College of Geographical Science, Faculty of Geographical Science and Engineering, Henan University
Chenhui Sun
College of Geographical Science, Faculty of Geographical Science and Engineering, Henan University
Yulong Bai
Department of Chemistry, Westlake University, 600 Dunyu Road, Hangzhou 310030, P. R. China
Yubang Wang
College of Geographical Science, Faculty of Geographical Science and Engineering, Henan University
Yifei Shi
College of Geographical Science, Faculty of Geographical Science and Engineering, Henan University
Lei Ma
Wei Zhang
Qing Ye
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences
Junhua Yan
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences
Keya Wang
Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences
Juemin Fu
Jigongshan National Nature Reserve
Wenzhi Du
Jigongshan National Nature Reserve
Denglong Ha
Jigongshan National Nature Reserve
Yuxi Ju
Jigongshan National Nature Reserve
Shiqiang Wan
College of Life Sciences/Hebei Basic Science Center for Biotic Interaction, Institute of Life Science and Green Development, Hebei University
Liang Hong
Centre for Clean Energy Technology, Faculty of Science
Yunting Fang
Chinese Academy of Sciences Key Laboratory of Forest Ecology and Silviculture, Institute of Applied Ecology, Chinese Academy of Sciences
Evan Siemann
Biosciences Department, Rice University
Yiqi Luo
Peter B. Reich
Shenglei Fu
College of Geographical Science, Faculty of Geographical Science and Engineering, Henan University