Imbalanced phosphorus and nitrogen deposition in China's forests

Enzai Du,Wenxuan Han,Wim De Vries,Yuan Jiang,Xuejun Liu,Zhengbing Yan

doi:10.5194/acp-16-8571-2016

Abstract

Abstract. Acceleration of anthropogenic emissions in China has substantially increased nitrogen (N) deposition during the last 3 decades and may result in an imbalance of atmospheric N and phosphorus (P) inputs in terrestrial ecosystems. However, the status of P deposition in China is poorly understood. This study synthesized data on total P and total N concentrations in bulk precipitation and throughfall from published literature to assess the characteristics of P deposition, N deposition and N : P deposition ratio in China's forests. Our results show relatively high mean rates of bulk P deposition (0.38 kg P ha−1 yr−1) and total P deposition (0.69 kg P ha−1 yr−1), but they were accompanied by even more elevated N inputs via bulk deposition (16.5 kg N ha−1 yr−1) and total deposition (21.6 kg N ha−1 yr−1), resulting in high N : P ratios in bulk deposition (44.4) and total deposition (32.8). Based on the difference between total deposition and bulk deposition, canopy-captured dry P and N deposition was estimated to be 0.31 kg P ha−1 yr−1 and 5.1 kg N ha−1 yr−1, respectively. We found significantly higher P deposition and lower N : P ratios at sites nearby than those far from semiarid regions. The estimated bulk and total deposition of P and N both showed a significant power-law increase with decreasing distance to the nearest large cities either in the areas nearby or far from semiarid regions. Our results suggest an anthropogenic alternation of regional P and N cycling, which may shift large areas of China's forests towards human-induced P limitation especially in southern China.

Highlights

Nitrogen (N) and phosphorus (P) are essential macronutrients, both of which widely limit primary productivity across terrestrial ecosystems (Elser et al, 2007; Vitousek et al, 2010)
Bulk P deposition and total P deposition were characterized by a log-normal distribution (Shapiro–Wilk normality test, p > 0.10), showing geometric means at 0.38 (0.21–0.57) and 0.69 (0.40–1.20) kg P ha−1 yr−1, respectively
Our results show elevated atmospheric P deposition in China’s forests, but it is accompanied by even more elevated N deposition

Summary

Introduction

Nitrogen (N) and phosphorus (P) are essential macronutrients, both of which widely limit primary productivity across terrestrial ecosystems (Elser et al, 2007; Vitousek et al, 2010). External N inputs to terrestrial ecosystems are driven by biological N fixation and atmospheric deposition, the latter being increasingly important (Cleveland et al, 2013). Acceleration of anthropogenic N emissions has substantially increased N deposition in China during the last 3 decades and aroused widespread concerns about the consequent impacts on various ecosystems (Liu et al, 2011, 2013; Cui et al, 2013). Soil P availability in terrestrial ecosystems is primarily driven by mineral weathering and atmospheric deposition (Vitousek et al, 2010; Cleveland et al, 2013). More recent assessment of observed and modelled P deposition rates on a global scale (Mahowald et al, 2008; Wang et al, 2015) shows a range of 0.01–1.0 kg P ha−1 yr−1 on land. Despite the significant role of P deposition, its status and characteristics are poorly understood in China

Results

Discussion

Conclusion