Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari

In August 2005, when the surface and subsoils were dry, the ambient CO2 efflux was negative and low during the daytime (−6.15 mg C m2 h−1). When 8 mm rainfall equivalent of water was added to the surface there was an immediate uptake of CO2 during the daytime at rates up to 75 mg C m2 h−1 demonstrating that rates of net photosynthesis are greatly enhanced by available moisture. In contrast, in May 2006 following a prolonged wet period when the subsoil was moist, there was a net positive efflux of CO2 from the soil at rates of up to 60 mg C m2 h−1 irrespective of whether the surface soil was moist or not. This is consistent with subsoil heterotrophic bacterial respiration becoming an important contributor to soil efflux.