The temperature sensitivity of organic carbon mineralization is affected by exogenous carbon inputs and soil organic carbon content

- Effects of C inputs on CO2 production varied with SOC content and substrate types.
- Soils with a higher SOC content was less responsive to C inputs.
- Carbon inputs increased Q10 of the stable C pool in higher SOC soils.
- Temperature sensitivity of mineralization as affected by C inputs varied with SOC content.

Temperature sensitivity of organic carbon (C) mineralization is affected by C inputs, but predicting the magnitude of the response remains a challenge. We investigated how temperature and exogenous C inputs affected the apparent organic C mineralization in soils with a range of soil organic C (SOC) contents. Soils with 2.9, 4.0, and 6.8% SOC content were incubated with or without C sources (either plant residues or glucose), at two temperatures (15 or 25 °C) for 120 days. Apparent organic C mineralization was significantly affected by SOC content and C inputs. Cumulative CO2 production in soils with a higher SOC content was less sensitive to C inputs. Glucose was always more effective in stimulating CO2 production than plant residue. Without exogenous C inputs, the temperature sensitivity of organic C mineralization (described by Q10 value) was higher in the 4.0% SOC soil (2.31) than in the 2.9% (1.12) and 6.8% SOC soils (1.30). The addition of exogenous C decreased Q10 values by up to 131% in the 4.0% SOC soil, which was not observed in other two soils. In general, C inputs increased the Q10 of the estimated active (Ca) and stable C (Cs) pools in all the tested soils, especially the Cs pool in the 4.0 and 6.8% SOC soils. Results indicated that the effect of C inputs on apparent organic C mineralization (either stimulatory or inhibitory) is influenced by SOC content and C source, and that temperature sensitivity of organic C mineralization in the presence of exogenous C is highly sensitive to SOC content.