Effects of long-term nitrogen deposition on phosphorus leaching dynamics in a mature tropical forest
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Elevated anthropogenic nitrogen (N) deposition is suggested to affect ecosystem phosphorus (P) cycling through altered biotic P demand and soil acidification. To date, however, there has been little information on how long-term N deposition regulates P fluxes in tropical forests, where P is often depleted. To address this question, we conducted a long-term N addition experiment in a mature tropical forest in southern China, using the following N treatments: 0, 50, 100, and 150 kg N ha−1 year−1. We hypothesized that (i) tropical forest ecosystems have conservative P cycling with low P output, and (ii) long-term N addition decreases total dissolved phosphorus (TDP) leaching losses due to reduced litter decomposition rates and stimulated P sorption deriving from accelerated soil acidification. As hypothesized, we demonstrated a closed P cycling with low leaching outputs in our forest. Under experimental N addition, TDP flux in throughfall was significantly reduced, suggesting that N addition may result in a less internal P recycling. Contrary to our hypothesis, N addition did not decrease TDP leaching, despite reduced litter decomposition and accelerated soil acidification. We find that N addition might have negative impacts on biological P uptake without affecting TDP leaching, and that the amount of TDP leaching from soil could be lower than a minimum concentration for TDP retention. Overall, we conclude that long-term N deposition does not necessarily decrease P effluxes from tropical forest ecosystems with conservative P cycling.
KeywordsNitrogen deposition Phosphorus cycling Phosphorus leaching Tropical forest
This study was funded by the National Basic Research Program of China (2014CB954400) and National Natural Science Foundation of China (Nos. 41731176, 41473112, 31370498) and Youth Innovation Promotion Association CAS (2015287). We wish to thank Lijie Deng, Shaoming Cai and Quannian Nie for skillful field work. We also thank Xiaoying You and Shaowei Chen for laboratory work. We would like to express our sincere appreciation to the three anonymous reviewers and the editor for their insightful comments, which have greatly aided us in improving the quality of our paper.
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