Abstract
AbstractArid 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.
Highlights
Arid and semiarid landscapes comprise ~40% of the earths’ terrestrial surface and are expected to be susceptible to global change
The CO2 source value was on average 4.4‰ higher for interspace than Larrea soils, which contained a greater percentage of depleted organic C (Table 1)
We found that high surface temperatures (>69 ̊C) support the greatest rates of CO2 efflux from dry soils under summer conditions
Summary
Arid and semiarid landscapes comprise ~40% of the earths’ terrestrial surface and are expected to be susceptible to global change. Recent research has demonstrated that in arid ecosystems with alkaline soils derived from calcareous parent material, abiotic (non-respiratory) CO2 exchange may be an overlooked aspect of the C cycle [Serrano-Oritz et al, 2010] Though ignoring this flux may lead to overestimates of biological respiration, whether or not this process represents a meaningful C sink is currently debated [Schlesinger, 2016]. Arid soils are known to represent a major global carbonate reservoir [Eswaran et al, 2000], and carbonate concentrations in soil can exceed organic C by an order of magnitude or more [Stevenson and Verburg, 2006] Given that this flux can apparently be moderated by environmental variables such as atmospheric CO2 concentrations, temperature and rainfall distribution [Hamerlynck et al, 2013]- and that these variables are highly susceptible to change under future climate- detailed description of the process and mechanisms is a pressing priority
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