Trace gas fluxes and nitrogen cycling along an elevation sequence of tropical montane forests in Central Sulawesi, Indonesia

Abstract

Studies on soil‐atmosphere flux of N 2 O, NO and CH 4 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 N 2 O 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 δ 15 N signals in litterfall and soil organic matter) show that the annual N 2 O + NO emissions could be explained by the inherent N status of these forests. In a test of indices of N cycling to explain N 2 O and NO fluxes, the robustness of litterfall C/N and litterfall N was confirmed and the δ 15 N signal of litterfall emerged as promising driver for regional and global biogeochemical models that predict N 2 O + NO emissions from soil.