Influencing factors and partitioning methods of carbonate contribution to CO2 emissions from calcareous soils

In calcareous soils, recent studies have shown that soil-derived CO2 originates from both soil organic carbon (SOC) decomposition and soil inorganic carbon (SIC) dissolution, a fact often ignored in earlier studies. This may lead to overestimation of the CO2 emissions from SOC decomposition. In calcareous soils, there is a chemical balance between precipitation and dissolution of CaCO3-CO2-HCO 3 − , which is affected by soil environmental factors (moisture, temperature, pH and depth), root growth (rhizosphere effect) and agricultural measures (organic materials input, nitrogen fertilization and straw removal). In this paper, we first introduced the contribution of SIC dissolution to CO2 emissions from calcareous soils and their driving factors. Second, we reviewed the methods to distinguish two CO2 sources released from calcareous soils and quantify the 13C fractionation coefficient between SIC and SIC-derived CO2 and between SOC and SOC-derived CO2, and to partition three CO2 sources released from soils with plants and organic materials input. Finally, we proposed methods for accurately distinguishing three CO2 sources released from calcareous soils. This review helps to improve the accuracy of soil C balance assessment in calcareous soils, and also proposes the direction of further investigations on SIC-derived CO2 emissions responses to abiotic factors and agricultural measures.