BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-3931-2013 Long-term nitrogen addition decreases carbon leaching in a nitrogen-rich forest ecosystem Lu X. 1 Gilliam F. S. 2 Yu G. 3 Li L. 4 Mao Q. 1 Chen H. 1 Mo J. 1 Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China Department of Biological Sciences, Marshall University, Huntington, West Virginia, 25755-2510, USA Institute of Geographical Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China State Key Laboratory of Vegetation Environmental Change, Institute of Botany, Chinese Academy of Sciences, Xiangshan, Beijing, 100093, China 18 06 2013 10 6 3931 3941 Copyright: © 2013 X. Lu et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/3931/2013/bg-10-3931-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/3931/2013/bg-10-3931-2013.pdf

Dissolved organic carbon (DOC) plays a critical role in the carbon (C) cycle of forest soils, and has been recently connected with global increases in nitrogen (N) deposition. Most studies on effects of elevated N deposition on DOC have been carried out in N-limited temperate regions, with far fewer data available from N-rich ecosystems, especially in the context of chronically elevated N deposition. Furthermore, mechanisms for excess N-induced changes of DOC dynamics have been suggested to be different between the two kinds of ecosystems, because of the different ecosystem N status. The purpose of this study was to experimentally examine how long-term N addition affects DOC dynamics below the primary rooting zones (the upper 20 cm soils) in typically N-rich lowland tropical forests. We have a primary assumption that long-term continuous N addition minimally affects DOC concentrations and effluxes in N-rich tropical forests. Experimental N addition was administered at the following levels: 0, 50, 100 and 150 kg N ha<sup>−1</sup> yr<sup>−1</sup>, respectively. Results showed that seven years of N addition significantly decreased DOC concentrations in soil solution, and chemo-physical controls (solution acidity change and soil sorption) rather than biological controls may mainly account for the decreases, in contrast to other forests. We further found that N addition greatly decreased annual DOC effluxes from the primary rooting zone and increased water-extractable DOC in soils. Our results suggest that long-term N deposition could increase soil C sequestration in the upper soils by decreasing DOC efflux from that layer in N-rich ecosystems, a novel mechanism for continued accumulation of soil C in old-growth forests.

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