Although soil carbon dioxide (CO2) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations and factors controlling soil CO2 efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO2 efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact tropical rainforest in Sarawak, Malaysia. Soil CO2 efflux varied widely in space; the range of variation averaged 17.4 μmol m-2 s-1 in total. While most CO2 flux rates were under 10 μmol m-2 s-1, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little spatial dependence in soil CO2 efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation in CO2 efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO2 efflux, estimated from the relationship between CO2 efflux and SMC at 30 cm depth, was 165 mol m-2 year-1 (1,986 g C m-2 year-1). As this area is known to suffer severe drought every 4-5 years caused by the El Nino-Southern Oscillation, the results suggest that an unpredictable dry period might affect soil CO2 efflux, leading an annual variation in soil C balance.
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