Threshold and multiple indicators for nitrogen saturation in subtropical forests.

Yu Q; Duan L; Yu L; Chen X; Si G; Ke P; Ye Z; Mulder J

doi:10.1016/j.envpol.2018.06.001

Back

Journal article

Threshold and multiple indicators for nitrogen saturation in subtropical forests.

Yu Q State Key Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China.
Duan L State Key Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China; Collaborative Innovation Centre for Regional Environmental Quality, Tsinghua University, Beijing, 100084, China. Electronic address: lduan@tsinghua.edu.cn.
Yu L Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, NO-1432 Ås, Norway; Laboratory for Air Pollution & Environmental Technology, Empa, Ueberlandstr. 129, CH-8600 Duebendorf, Switzerland.
Chen X Air Environmental Modeling and Pollution Controlling Key Laboratory of Sichuan Education Institutes, College of Resources and Environment, Chengdu University of Information Technology, Chengdu, 610225, China.
Si G State Key Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China.
Ke P State Key Laboratory of Environmental Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing, 100084, China.
Ye Z Air Environmental Modeling and Pollution Controlling Key Laboratory of Sichuan Education Institutes, College of Resources and Environment, Chengdu University of Information Technology, Chengdu, 610225, China.
Mulder J Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Box 5003, NO-1432 Ås, Norway.

2018-06-15

Published in:

Environmental pollution (Barking, Essex : 1987). - 2018

English The influence of nitrogen (N) deposition on forest ecosystems largely depend on the N status. Developing threshold and practical indicators for N saturation in subtropical forests, with extremely high N deposition, would both enhance forest management and the assessments of global N balance and carbon (C) sequestration. Here, we quantified the N mass balance and assessed current N status at a number of subtropical forest sites in South China, using both N content, C/N ratio, and 15N natural abundance (δ15N) as potential indicators of N saturation. Among the studied sites, N deposition ranged from 13.8 to 113 kg N ha-1 yr-1 in throughfall, and was dominated by ammonium (NH4+). The threshold for N leaching in subtropical forest was first found to be 26-36 kg N ha-1 yr-1, which was 160% higher than in temperate forest (based on prescribed minimum). This indicates that critical parameter inputs in global models of the impact of N deposition are in need of revision, based on specific ecosystem characteristics. We found a critical C/N ratio of 20 for the O/A horizon as indicator of N saturation. Foliar N content and δ15N were positively correlated with N deposition and were well suited to indicate regional N status. The δ15N enrichment factor (Ɛfoli/So2, δ15Nfoliage - δ15NSoil2) was between -10‰ and -1‰, and had similar trend to those obtained from other regions with increasing N deposition. These suggest that the enrichment factor could be used to investigate the influence of N deposition in forest ecosystems, regardless of spatial heterogeneity in δ15N of N input, soil N availability and geomorphology.

Language