N₂O emission from tropical forest soils of Australia

Abstract

Three different tropical rain forest sites (Kauri Creek, Lake Eacham, and Massey Creek) on the Atherton Tablelands, Queensland, Australia, were investigated for the magnitude of N 2 O emission from soils during different seasons, that is, wet season, dry season, and transition periods. Highest mean N 2 O emission rates were observed for soils derived from granite at the Kauri Creek site with 74.5±25.2 μg N 2 O‐N m −2 h −1 , whereas for soils derived from Metamorphics (Lake Eacham site) mean N 2 O emission rates were much lower (13.1±1.1 μg N 2 O‐N m −2 h −1 ). For the Massey Creek site, with soils derived from Rhyolite, a mean annual N 2 O emission rate of 46. ±1.1 μg N 2 O‐N m −2 h −1 was calculated. The mean annual N 2 O emission rate calculated for all three sites over the entire observation period was 39.0 μg N 2 O‐N m −2 h −1 and thus at the high end of reports from tropical rain forest soils. N 2 O emission rates showed at all sites pronounced temporal as well as spatial variability. The magnitude of N 2 O emissions was strongly linked to rainfall events; that is, N 2 O emissions strongly increased approximately 6–8 hours after precipitation. Correlation analysis confirmed the strong dependency of N 2 O emissions on changes in soil moisture, whereas changes in soil temperature did not mediate considerable changes in N 2 O fluxes. Spatial variability of N 2 O fluxes on a site scale could be explained best by differences in water‐filled pore space, CO 2 emission, and C/N ratio of the soil. On the basis of all published N 2 O flux rates from tropical rain forest soils we recalculated the contribution of such forests to the global atmospheric N 2 O budget and come up with a figure of 3.55 Tg N 2 O‐N yr −1 , which is approximately 50% higher than reported by others.