Abstract. Tropical forests are critical for maintaining the global carbon balance and mitigating climate change, yet their exchange of greenhouse gases with the atmosphere remains understudied, particularly for methane (CH4) and nitrous oxide (N2O). This study reports on continuous measurements of CH4 and N2O fluxes at the ecosystem and soil levels, respectively through eddy covariance and an automated chamber technique, in a wet tropical forest in French Guiana over a period of 26 months. We studied the magnitude of CH4 and N2O fluxes and their drivers (climatic variables) during two extreme periods, the driest and wettest seasons. Seasonal ecosystem fluxes showed near-zero net CH4 uptake during the driest season and emissions occurring during the wettest season that were larger in magnitude than the uptake. Meanwhile, N2O emissions were of similar magnitudes in both seasons. Some upland soils within the footprint of the eddy covariance tower emitted N2O in both seasons, although these fluxes were particularly small. None of the measured climatic variables could explain this soil N2O flux variation. In contrast, the upland soils were characterised by CH4 uptake. Overall, seasonal ecosystem CH4 and N2O fluxes, as well as seasonal upland soil CH4 fluxes, were partially explained by seasonal variations in soil water content and global radiation. In addition to the upland soil fluxes studied, the magnitude and sign of the net ecosystem fluxes of CH4 and N2O were likely due to outgassing from aboveground biomass and the presence of seasonally flooded areas within the footprint of the eddy covariance system. Further studies of other ecosystem compartments in different forest habitats are needed to better understand the temporal variations in CH4 and N2O fluxes in wet tropical forests.
Bréchet et al. (Thu,) studied this question.
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