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

Abstract

Over 1 year we followed the seasonal variations of N2O and CH4 fluxes at a tropical rain forest site in Australia. In addition, meteorological parameters, litter fall and decomposition, plant species composition, and concentrations of NH4+/NO3− in the soil and N2O and CH4 in the soil atmosphere were measured. N2O 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 N2O‐N m−2 h−1). N2O emissions were positively correlated to N2O‐concentrations in the soil profile and to moisture, but not to concentrations of NH4+ and NO3−. The annual emission of N2O (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 N2O emissions between different years indicate that the interannual variability of N2O emissions from rain forest soils cannot be neglected. With regard to CH4 the soil functioned throughout the entire year as a significant sink. Rates of CH4 uptake during the dry period (35–68 μg CH4 m−2 h−1) were higher as compared to the wet period (4–45 μg CH4 m−2 h−1). A close linear correlation between soil moisture and magnitude of CH4 uptake was found. The calculated annual CH4 uptake (N = 6090) is 3.2 kg CH4 ha−1 yr−1. This implies that tropical rain forest soils function as significant sinks for atmospheric CH4 on a global scale.