Low N2O and variable CH4 fluxes from tropical forest soils of the Congo Basin

The Congo Basin is home to the second largest stretch of continuous tropical forest, but the magnitude of greenhouse fluxes are poorly understood. Here the authors analyze gas samples and find the region is not actually a hotspot of N2O emissions. Globally, tropical forests are assumed to be an important source of atmospheric nitrous oxide (N2O) and sink for methane (CH4). Yet, although the Congo Basin comprises the second largest tropical forest and is considered the most pristine large basin left on Earth, in situ N2O and CH4 flux measurements are scarce. Here, we provide multi-year data derived from on-ground soil flux (n = 1558) and riverine dissolved gas concentration (n = 332) measurements spanning montane, swamp, and lowland forests. Each forest type core monitoring site was sampled at least for one hydrological year between 2016 - 2020 at a frequency of 7-14 days. We estimate a terrestrial CH4 uptake (in kg CH4-C ha(-1) yr(-1)) for montane (-4.28) and lowland forests (-3.52) and a massive CH4 release from swamp forests (non-inundated 2.68; inundated 341). All investigated forest types were a N2O source (except for inundated swamp forest) with 0.93, 1.56, 3.5, and -0.19 kg N2O-N ha(-1) yr(-1) for montane, lowland, non-inundated swamp, and inundated swamp forests, respectively.

Automated summary

The Congo Basin, the second largest tropical forest region, is not a hotspot of N2O emissions, and different forest types in the region vary in their uptake and release of CH4 and N2O.