Effect of underground fungus-growing termites on carbon dioxide emission at the point- and landscape-scales in an African savanna

Abstract

1. The rate of CO2 emission by two major termite species (Ancistrotermes cavithorax and Odontotermes n. pauperans) was studied in a West African savanna (Lamto, Côte d'Ivoire). First, in three major savanna types (grassy, shrubby and woody savannas), CO2 emission from the soil surface was measured using a closed container system. Control soil without termite fungus-comb chambers, and soil of eroded termite mound with or without Odontotermes fungus-comb chambers was sampled in each savanna type. Second, the mass-specific respiration rate of the different components of termite fungus-comb chambers (i.e. workers, soldiers, fungus comb and chamber walls) was measured under laboratory conditions. CO2 emission by termites at the landscape-scale was computed from both field biomass data and laboratory measurements. 2. Whatever the savanna type, CO2 emission from the soil surface was not different between control soil and soil of eroded termite mound without termite fungus-comb chambers, but was significantly higher in areas with fungus-comb chambers than in areas without fungus-comb chambers (10-19 μmol CO2 m-2 s-1 vs 5-10 μmol CO2 m-2 s-1). 3. The mass-specific respiration rates were higher for individuals of O. pauperans than for individuals of A. cavithorax. Total respiration rate from an individual fungus-comb chamber was around 56 and 143 μmol CO2 h-1 for Ancistrotermes and Odontotermes, respectively. 4. Despite a low mass-specific respiration rate, fungus comb accounted for 51% of the total respiration flux from whole chambers in Odontotermes and for 82% in Ancistrotermes. The laboratory-derived respiration rate from individual Odontotermes chambers was consistent with the field estimates. 5. At the landscape-scale, the CO2 emission due to A. cavithorax and O. pauperans was 0.022 and 0.050 μmol CO2 m-2 s-1, respectively. This total (27.2 g C m-2 years-1) represented 4.9% of the total above-ground net primary production in this ecosystem and 11.3% of the carbon not mineralized by annual fires.