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 CO2 exchange via a diel cycle of carbonate dissolution and exsolution. We used a Keeling plot approach to determine the substrate δ13C of CO2 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 CO2 substrate had δ13C values of −19.4 ± 4.2‰, indicative of respiration of organic material (soil organic matter = −23.1 ± 0.8‰). CO2 flux increased with temperature; maximum fluxes occurred above 60°C, where δ13CO2 substrate (−7.2‰ ± 2.8‰) approached soil carbonate values (0.2 ± 0.2‰). In wet soils, CO2 emissions were not temperature dependent, and δ13CO2 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 CO2 emissions from alkaline desert soils derived from an abiotic source and that diurnal emission patterns are strongly driven by surface temperature.