Long-term nitrogen addition decreases carbon leaching in a nitrogen-rich forest ecosystem

[摘要] Dissolved organic carbon (DOC) plays a critical role in the carbon (C) cycleof forest soils, and has been recently connected with global increases innitrogen (N) deposition. Most studies on effects of elevated N deposition onDOC have been carried out in N-limited temperate regions, with far fewerdata available from N-rich ecosystems, especially in the context ofchronically elevated N deposition. Furthermore, mechanisms for excessN-induced changes of DOC dynamics have been suggested to be differentbetween the two kinds of ecosystems, because of the different ecosystem Nstatus. The purpose of this study was to experimentally examine howlong-term N addition affects DOC dynamics below the primary rooting zones(the upper 20 cm soils) in typically N-rich lowland tropical forests. Wehave a primary assumption that long-term continuous N addition minimallyaffects DOC concentrations and effluxes in N-rich tropical forests.Experimental N addition was administered at the following levels: 0, 50, 100and 150 kg N ha⁻¹ yr⁻¹, respectively. Results showed that sevenyears of N addition significantly decreased DOC concentrations in soilsolution, and chemo-physical controls (solution acidity change and soilsorption) rather than biological controls may mainly account for thedecreases, in contrast to other forests. We further found that N additiongreatly decreased annual DOC effluxes from the primary rooting zone andincreased water-extractable DOC in soils. Our results suggest that long-termN deposition could increase soil C sequestration in the upper soils bydecreasing DOC efflux from that layer in N-rich ecosystems, a novelmechanism for continued accumulation of soil C in old-growth forests.

[学科分类] 地球化学与岩石