Imbalanced phosphorus and nitrogen deposition in China's forests

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 kgNha(-1) yr(-1))and total deposition (21.6 kgNha(-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 kgNha(-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.