Temperature dependence of CO2 emissions rates and isotopic signature from a calcareous soil

• SIC contributes to CO2 emissions from calcareous soils.
• δ13C of emitted CO2 was dependent of temperature and duration of incubation.
• Isotopic calculations of the contribution of SIC to CO2 is not straightforward.
• The dynamics of SOC and SIC are not independent.

In the context of climate change, studies have focused on the temperature dependence of soil CO2 emissions. Although calcareous soils cover over 30% of the earth's land surface, few studies have considered calcareous soils where soil inorganic carbon (SIC) makes the analysis of the C fluxes at the soil to air interface more complex.This study tested how temperature could affect the contributions of soil organic carbon (SOC) and SIC to the CO2 emitted from a calcareous soil. The soil pH, CO2 emissions and δ13C signatures of CO2 were measured after soil incubations at 4 temperatures (20 °C, 30 °C, 40 °C and 50 °C).The CO2 emissions and the δ13C signature of the emitted CO2 increased with temperature. The proportion of SIC-derived CO2 in these emissions seemed to be stimulated by temperature.Three processes were discussed: (1) isotopic fractionations, (2) temperature impacts on SIC- and SOC-derived CO2, and (3) isotope exchanges between SIC- and SOC-derived CO2. The use of δ13C signature analysis to determine the contribution of SIC and SOC to the total CO2 emissions from soil is not straightforward. An increase in the SIC signature of emitted CO2 does not directly imply an increase in SIC as a source of CO2.