Assessing CO₂ and CH₄ fluxes from mounds of African fungus-growing termites

Abstract

Abstract. Termites play an essential role in decomposing dead plant material in tropical ecosystems and are thus major sources of gaseous C emissions in many environments. In African savannas, fungus-growing termites are among the ecologically most influential termite species. We studied the gas exchange from mounds of two closely related fungus-growing species (Macrotermes subhyalinus and M. michaelseni, respectively) in shaded and open habitats together with soil fluxes around the mounds. The fluxes from active termite mounds varied from 116 to 2105 mg CO2-C m-2 h-1 for CO2 and from 0.06 to 3.66 mg CH4-C m-2 h-1 for CH4 fluxes. Mound CO2 fluxes varied seasonally with a 64 % decrease and 35 % increase in the fluxes from dry to wet season at the open grassland and shaded bushland sites, respectively. During the wet season, the CO2 fluxes were significantly correlated with termite mound volume. The diurnal measurements from two M. michaelseni mounds suggest that the gas fluxes peak during daytime and midnight supporting the previously presented model of thermally driven air circulation inside the mound and possibly enhanced ventilation during the night by the opening of foraging routes. The stability of the mound gas fluxes over diurnal and annual scales coincides with the constant nature of the nest internal gas and thermal environment that guarantees continuously favorable conditions for the fungal symbiont. Soil fluxes of both CO2 and CH4 were enhanced at up to 2 m distance from the mounds compared to the local soil respiration, indicating that, in addition to mound ventilation structures, a small proportion of the produced metabolic gases leave the nest also via surrounding soils.

Mound architecture and season affect concentrations of CO2, CH4 and N2O in nests of African fungus‐growing termites

“…To compare nest internal gas concentrations with the mound size, the height and width of each mound were measured in two directions (South-West and North-East). Based on these measured parameters, the volume of the aboveground mound was estimated using the equation (Equation 1) defined in Räsänen et al (2023):…”

“…There, the plant cell walls are broken down into simple sugars by actions of the Termitomyces symbionts in wellaerated fungus combs and by the intestinal bacterial flora during two subsequent passages through guts of termite workers (Badertscher et al, 1983;Nobre & Aanen, 2012;Poulsen et al, 2014;. As a result of effective decomposition, termite nests commonly emit an order of magnitude higher amounts of carbon dioxide (CO 2 ) than the surrounding savanna soils (Konaté et al, 2003;Räsänen et al, 2023;Van Asperen et al, 2021).…”