Abstract
Abstract. Soil respiration is an important carbon flux and key process determining the net ecosystem production of terrestrial ecosystems. To address the 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 annually in two dominant forest types (lowland and montane) of the Congo Basin over 2 years at varying temporal resolution. Soil CO2 fluxes from the Congo Basin resulted in 3.45 ± 1.14 and 3.13 ± 1.22 µmol CO2 m−2 s−1 for lowland and montane forests, respectively. Soil CO2 fluxes 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. Smaller differences of δ13C values of leaf litter, 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 seem to be different, i.e., soil moisture for montane forest and C availability for lowland forest.
Highlights
Soil basal respiration, the sum of carbon dioxide (CO2) produced both autotrophically by roots and heterotrophically by bacterial and fungal respiration, represents the biggest natural transfer of carbon (C) from the terrestrial biosphere to the atmosphere (Raich and Schlesinger, 1992)
A decrease in water-filled pore space (WFPS) was observed during dry season in the montane forest (Fig. 2b)
The only reported soil CO2 fluxes from a tropical forest in Africa in recent years are from Kenya (Arias-Navarro et al, 2017; Werner et al, 2007), and they were rather low compared to our flux rates
Summary
The sum of carbon dioxide (CO2) produced both autotrophically by roots and heterotrophically by bacterial and fungal respiration, represents the biggest natural transfer of carbon (C) from the terrestrial biosphere to the atmosphere (Raich and Schlesinger, 1992). Soil temperature affects biological activity, whereas soil moisture affects the diffusion of C substrate, atmospheric oxygen, and respired CO2 through soil pores (Janssens et al, 1998; Doff Sotta et al, 2004; Sousa Neto et al, 2011; Courtois et al, 2018). Soil pH (Courtois et al, 2018), through its effects on microbial communities, and root density can affect soil CO2 production (Janssens et al, 1998). Another important driver is photosynthetic activity, as it describes the rate of carbohydrate supply from leaves to roots, where both root
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