Spatial Variation of Soil CO 2 , CH 4 and N 2 O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield
The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO 2 , methane—CH 4 and nitrous oxide—N 2 O) remains poorly understood in highly complex ecosystems such as tropical forests. Here, we used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO 2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH 4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N 2 O and N 2 O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This initial work describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns.