Seasonal variability of N2O emissions and CH4 uptake by tropical rainforest soils of Queensland, Australia

Over 1 year we followed the seasonal variations of N 2 O and CH 4 fluxes at a tropical rain forest site in Australia. In addition, meteorological parameters, litter fall and decomposition, plant species composition, and concentrations of NH 4 + /NO 3 − in the soil and N 2 O and CH 4 in the soil atmosphere were measured. N 2 O emissions showed a pronounced seasonal pattern with highest rates in the wet season (108.6 μg N m −2 h −1 ) and significantly lower rates during dry season (mostly <10 μg N 2 O‐N m −2 h −1 ). N 2 O emissions were positively correlated to N 2 O‐concentrations in the soil profile and to moisture, but not to concentrations of NH 4 + and NO 3 − . The annual emission of N 2 O (N = 6015) was 0.97 kg N ha −1 yr −1 , and, thus, approximately 7 times lower than a previous estimate for the year 2000. The marked differences in N 2 O emissions between different years indicate that the interannual variability of N 2 O emissions from rain forest soils cannot be neglected. With regard to CH 4 the soil functioned throughout the entire year as a significant sink. Rates of CH 4 uptake during the dry period (35–68 μg CH 4 m −2 h −1 ) were higher as compared to the wet period (4–45 μg CH 4 m −2 h −1 ). A close linear correlation between soil moisture and magnitude of CH 4 uptake was found. The calculated annual CH 4 uptake (N = 6090) is 3.2 kg CH 4 ha −1 yr −1 . This implies that tropical rain forest soils function as significant sinks for atmospheric CH 4 on a global scale.