Trace gas fluxes and nitrogen cycling along an elevation sequence of tropical montane forests in Central Sulawesi, Indonesia
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 Studies on soil-atmosphere flux of N2O, NO and CH4 in tropical forests have mainly focused on tropical lowland forests. Here we present the first intensive study of trace gas fluxes along an elevation sequence of tropical montane forests ranging from 1190 m to 2470 m elevation in Central Sulawesi, Indonesia. Using chamber techniques, we measured monthly flux rates and controlling factors on three elevations, each with three replicate plots for 1 year. Annual N2O fluxes ranged from 0.29 kg N ha(-1) yr(-1) at 1800 m to 1.01 kg N ha(-1) yr(-1) at 2470 m and 1.11 kg N ha(-1) yr(-1) at 1190 m, while annual NO fluxes ranged from 0.17 kg N ha(-1) yr(-1) at 1800 m, to 0.18 kg N ha(-1) yr(-1) at 2470 m and 0.48 kg N ha(-1) yr(-1) at 1190 m. Methane uptake ranged from 1.45 kg C ha(-1) yr(-1) at 2470 m to 2.45 kg C ha(-1) yr(-1) at 1190 m and 3.32 kg C ha(-1) yr(-1) at 1800 m. At the highest elevation, methane uptake was affected by the thick organic layer present at the surface of the soil. Several lines of evidence ( soil N stocks, extractable inorganic N, litterfall mass, litterfall-N and delta N-15 signals in litterfall and soil organic matter) show that the annual N2O + NO emissions could be explained by the inherent N status of these forests. In a test of indices of N cycling to explain N2O and NO fluxes, the robustness of litterfall C/N and litterfall N was confirmed and the delta N-15 signal of litterfall emerged as promising driver for regional and global biogeochemical models that predict N2O + NO emissions from soil.
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