Effects of Litter Inputs on N2O Emissions from a Tropical Rainforest in Southwest China

Litter inputs are expected to have a strong impact on soil N2O efflux. This study aimed to assess the effects of the litter decomposition process and nutrient efflux from litter to soil on soil N2O efflux in a tropical rainforest. A paired study with a control (L) treatment and a litter-removed (NL) treatment was followed for 2 years, continuously monitoring the effects of these treatments on soil N2O efflux, fresh litter input, decomposed litter carbon (LCI) and nitrogen (LNI), soil nitrate (NO3 (-)-N), ammonium (NH4 (+)-N), dissolved organic carbon (DOC), and dissolved nitrogen (DN). Soil N2O flux was 0.48 and 0.32 kg N2O-N ha(-1) year(-1) for the L and NL treatments, respectively. Removing the litter caused a decrease in the annual soil N2O emission by 33%. The flux values from the litter layer were higher in the rainy season as compared to the dry season (2.10 +/- 0.28 vs. 1.44 +/- 0.35 mu g N m(-2) h(-1)). The N2O fluxes were significantly correlated with the soil NO3 (-)-N contents (P < 0.05), indicating that the N2O emission was derived mainly from denitrification as well as other NO3 (-) reduction processes. Suitable soil temperature and moisture sustained by rainfall were jointly attributed to the higher soil N2O fluxes of both treatments in the rainy season. The N2O fluxes from the L were mainly regulated by LCI, whereas those from the NL were dominated jointly by soil NO3 (-) content and temperature. The effects of LCI and LNI on the soil N2O fluxes were the greatest in the 2 months after litter decomposition. Our results show that litter may affect not only the variability in the quantity of N2O emitted, but also the mechanisms that govern N2O production. However, further studies are still required to elucidate the impacting mechanisms of litter decomposition on N2O emission from tropical forests.