Seasonality, drivers, and isotopic composition of soil CO<sub>2</sub> fluxes from tropical forests of the Congo Basin

Abstract

<jats:p>Abstract. Soil respiration is an important carbon flux and key process determining the net ecosystem production of terrestrial ecosystems. To address the enormous lack of quantification and understanding of seasonality in soil respiration of tropical forests in the Congo Basin, soil CO2 fluxes and potential controlling factors were measured for the first time annually in two dominant forest types (lowland and montane) of the Congo Basin during three years at varying temporal resolution. Soil CO2 fluxes from the Congo Basin resulted in 3.69 ± 1.22 and 3.82 ± 1.15 µmol CO2 m−2 s−1 for lowland and montane forests, respectively. Respiration in montane forest soils showed a clear seasonality with decreasing flux rates during the dry season. Montane forest soil CO2 fluxes were positively correlated with soil moisture while CO2 fluxes in the lowland forest were not. Paired ẟ13C values of soil organic carbon (SOC) and soil CO2 indicated that SOC in lowland forests is more decomposed than in montane forests, suggesting that respiration is controlled by C availability rather than environmental factors. In general, C in montane forests was more enriched in 13C throughout the whole cascade of carbon intake via photosynthesis, litterfall, SOC, and soil CO2 compared to lowland forests, pointing to a more open system. Even though soil CO2 fluxes are similarly high in lowland and montane forests of the Congo Basin, the drivers of them were different, i.e. soil moisture for montane forest and C availability for lowland forest. </jats:p>

Fluvial sediment export from pristine forested headwater catchments in the Congo Basin

“…This reinforces the idea that there is source limitation within events in the Miombo woodland, as no change in POM sources is visible throughout the whole rainy season and no shift of source material occurs between baseflow and storm flow conditions. In previous studies at the same sites, we reported the ranges of δ 13 C and C:N values from different potential source material within our catchments (Baumgartner et al, 2020(Baumgartner et al, , 2021. These ranges are plotted together with the values of sediment samples from this study (Fig.…”

“…1). Soils in the lowland forest are classified as deeply weathered Ferralsols (Van Ranst et al, 2010) with a loamy sand texture (Baumgartner et al, 2020). The catchment area has been estimated using the 30 m Shuttle Radar Topographic Mission (SRTM) derived digital elevation model (DEM, NASA JPL) and the GPS (GPSMAP 60CSx, Garmin, accuracy <5 m) coordinates of the flume position.…”

Conservative N cycling despite high atmospheric deposition in early successional African tropical lowland forests

“…In recent years, our understanding of N cycling in the central Congo basin has increased substantially (Bauters et al 2016(Bauters et al , 2018Baumgartner et al 2020;Gallarotti et al 2021). From these studies we know that the forests of the Congo basin receive high atmospheric N deposition (Bauters et al 2018) but, at the same time, show relatively low rates of N 2 O emission (Gallarotti et al 2021).…”