Temporal and spatial variations of soil carbon dioxide, methane, and nitrous oxide fluxes in a Southeast Asian tropical rainforest

Abstract

To clar ify the factors controlling temporal and spatial var iations of soil carbon diox-ide (CO2 methane (CH4 and nitrous oxide (N 2 O) fluxes, we investigated these gas fluxes and environmental factors in a tropical rainforest in Peninsular Malaysia. Tempo-ral var iation of CO 2 flux in a 2-ha plot was positively related to soil water condition and5 rainfall histor y. Spatially, CO 2 flux was negatively related to soil water condition. When CO2 flux hotspots were included, no other environmental factors such as soil C or N concentrations showed any significant correlation. Although the larger area sampled in the present study complicates explanations of spatial var iation of CO 2 flux, our results suppor t a previously repor ted bipolar relationship between the temporal and spatial10 patter ns of CO 2 flux and soil water condition obser ved at the study site in a smaller study plot. Flux of CH 4 was usually negative with little var iation, resulting in the soil at our study site functioning as a CH 4 sink. Both temporal and spatial var iations of CH 4 flux were positively related to the soil water condition. Soil N concentration was also related to the spatial distr ibution of CH4 flux. Some hotspots were obser ved, proba-15 bly due to CH 4 production by ter mites, and these hotspots obscured the relationship between both temporal and spatial var iations of CH4 flux and environmental factors. Temporal var iation of N2 O flux and soil N 2 O concentration was large and significantly related to the soil water condition, or in a str ict sense, to rainfall histor y. Thus, the rainfall patter n controlled wet seas on N 2 O production in soil and its soil surface flux.20 Spatially, large N 2 O emissions were detected in wet per iods at wetter and anaerobic locations, and were thus deter mined by soil physical proper ties. Our results showed that, even in Southeast Asian rainforests where distinct dr y and wet seasons do not ex-ist, var iation in the soil water condition related to rainfall histor y controlled the temporal var iations of soil CO2 flux, CH 4 uptake, and N 2 O emission. The soil water condition25 associated with soil hydraulic proper ties was also the impor tant controlling factor of the spatial distr ibutions of these gas fluxes.