Recalcitrant carbon controls the magnitude of soil organic matter mineralization in temperate forests of northern China

The large potential of the soil organic carbon (SOC) pool to sequester CO 2 from the atmosphere could greatly ameliorate the effect of future climate change. However, the quantity of carbon stored in terrestrial soils largely depends upon the magnitude of SOC mineralization. SOC mineralization constitutes an important part of the carbon cycle, and is driven by many biophysical variables, such as temperature and moisture. Soil samples of a pine forest, an oak forest, and a pine and oak mixed forest were incubated for 387 days under conditions with six temperature settings (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C) and three levels of soil moisture content (SMC, 30%, 60%, 90%). The instantaneous rate of mineralized SOC was periodically and automatically measured using a Li-Cor CO 2 analyzer. Based on the measured amount of mineralized SOC, carbon fractions were estimated separately via first-order kinetic one- and two-compartment models. During the 387 day incubation experiment, accumulative mineralized carbon ranged from 22.89 mg carbon (C) ·g − 1 SOC at 30 °C and 30% SMC for the mixed forest to 109.20 mg C·g − 1 SOC at 15 °C and 90% SMC for the oak forest. Mineralized recalcitrant carbon varied from 18.48 mg C·g − 1 SOC at 30 °C and 30% SMC for the mixed forest to 104.98 mg C·g − 1 SOC at 15 °C and 90% SMC for the oak forest, and contributed at least 80% to total mineralized carbon. Based on the results of this experiment, the soil organic matter of the pure broadleaved forest is more vulnerable to soil microbial degradation in northern China; most of the amount of the mineralized SOC derived from the recalcitrant carbon pool. Labile carbon fraction constitutes on average 0.4% of SOC across the three forest types and was rapidly digested by soil microbes in the early incubation stage. SOC mineralization markedly increased with soil moisture content, and correlated parabolically to temperature with the highest value at 15 °C. No significant interaction was detected among these variables in the present study.