Spatial Variation of Soil CO2, CH4 and N2O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield
The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO2, methane—CH4 and nitrous oxide—N2O) remains poorly understood in highly complex ecosystems such as tropical forests. 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. CO2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH4 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 N2O and N2O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study 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.
Keywordstropical forest GHG soil fluxes Guiana Shield soil characteristics spatial variation French Guiana
This research was supported by the European Research Council Synergy grant ERC-2013-SyG 610028-IMBALANCE-P. We thank the staff of the Nouragues station, managed by USR mixte LEEISA (CNRS; Cayenne), and the Paracou station, managed by UMR Ecofog (CIRAD, INRA; Kourou). Both research stations received support from “Investissement d’Avenir” grants managed by Agence Nationale de la Recherche (CEBA: ANR-10-LABX-25-01, ANAEE-France: ANR-11-INBS-0001). We thank the subject-matter editor Dr Butterbach-Bahl, Dr Teh and one anonymous reviewer for their comments on previous versions of this manuscript. We thank Nicola Arriga, Jan Segers and Fred Kockelbergh for building the chambers and for advice on the field measurements. We are grateful to Stanislas Talaga, Jérôme Levy-Valensky and Jean-Pierre Robert for their help in the field, to Oriol Grau and Vincent Freycon for the identification and characterization of each topographical position and to Margarethe Watzka for the gas analyses.
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