Contributions of Carbonates to Carbon Dioxide Release From a Calcareous Soil in Response to Experimental Warming

Abstract

Seasonal asymmetric warming is a distinguishing feature of climate change, which is not often considered when evaluating the effects of global change on terrestrial ecosystems. Responses of soil CO₂ efflux from organic and inorganic sources to asymmetric and symmetric warming are not well understood. A 5-year warming experiment was performed to evaluate the effects of symmetric and asymmetric warming on soil organic carbon (SOC)–derived and carbonate-derived effluxes from a calcareous soil in the karst region of southwestern China. On average, the carbonate-derived efflux represented 31% of the total CO₂ efflux in the six treatments. Warming of 2.0°C substantially stimulated soil CO₂ efflux from both sources, except for the carbonate-derived efflux in summer-autumn. Soil CO₂ efflux and SOC-derived efflux were appreciably reduced when ratios of warming in winter-spring to summer-autumn ratio of asymmetric warming (R_AW) increased, while no changes (full year or in summer-autumn) were found for the carbonate-derived efflux. However, soil CO₂ efflux from both sources were considerably enhanced in winter-spring with increasing R_AW values. Temperature sensitivity temperature coefficient (Q₁₀) of CO₂ efflux from both sources decreased with increasing R_AW values. The average Q₁₀ of SOC-derived efflux was 1.3 times greater that of the carbonate-derived efflux. Symmetric warming potentially overestimates CO₂ efflux from calcareous soils, compared with the projected asymmetric warming scenario, likely because of overestimation of SOC-derived effluxes in summer-autumn.