Soil carbon dioxide emissions from the Mojave desert: Isotopic evidence for a carbonate source

Abstract Arid soils represent a substantial carbonate pool and may participate in surface‐atmosphere CO 2 exchange via a diel cycle of carbonate dissolution and exsolution. We used a Keeling plot approach to determine the substrate δ 13 C of CO 2 emitted from carbonate‐dominated soils in the Mojave desert and found evidence for a nonrespiratory source that increased with surface temperature. In dry soils at 25–30°C, the CO 2 substrate had δ 13 C values of −19.4 ± 4.2‰, indicative of respiration of organic material (soil organic matter = −23.1 ± 0.8‰). CO 2 flux increased with temperature; maximum fluxes occurred above 60°C, where δ 13 CO 2 substrate (−7.2‰ ± 2.8‰) approached soil carbonate values (0.2 ± 0.2‰). In wet soils, CO 2 emissions were not temperature dependent, and δ 13 CO 2 substrate was lower in vegetated soils with higher flux rates, higher organic C content, and potential root respiration. These data provide the first direct evidence of CO 2 emissions from alkaline desert soils derived from an abiotic source and that diurnal emission patterns are strongly driven by surface temperature.