Abstract: Exogenous organic carbon input is one of the most important factors regulating the balance of soil organic carbon (SOC) input and output. The effects of adding exogenous carbon with different chemical structures to soils with different textures on the CO₂ emission from mineralization of organic carbon are still unclear. In this study, we added four kinds of exogenous carbon (sucrose, starch, cellulose and lignin) to red soil and sandy soil with different texture, and compared the impacts on CO₂ release rates, cumulative amount and its proportion of CO₂-C loss. The aim of our study is to provide new insights on how soil texture and chemical structure of exogenous carbon drive soil organic carbon turnover. Our results showed that exogenous carbon addition increased CO₂ release rates, cumulative amounts, and the proportion of C loss, with the magnitude of such impacts varying among different exogenous carbon treatments. Soil texture had significant effects on CO₂ release rates, cumulative amounts, and the proportion of C loss. There were significant interactions between exogenous carbon and soil texture. Sandy soil had higher CO₂release rates, cumulative amounts and C loss proportion than red soil. The dynamics of CO₂release rates differed among exogenous carbon treatments. The peak values of CO₂ release rate in the complexstructured organic carbon treatments were usually delayed as compared to sucrose addition. Our results suggest that the effects of exogenous carbon addition on the organic carbon mineralization are closely related to the chemical structure of exogenous organic carbon and soil texture.

Key words: exogenous carbon, soil texture, CO₂ release rate, red soil, sandy soil.