Thermal response of soil microbial respiration is positively associated with labile carbon content and soil microbial activity

The rate of substrate availability in mediating the response of soil microbial respiration rate (SMRR) relative to temperature was investigated using soils from southern Inner Mongolia. Two independent experiments were performed: the first one was to provide natural soils with different soil water contents (non-incubation experiments), and the second one was to incubate soils under two temperature regimes (10 °C and 30 °C) and two moisture regimes (35% and 75% water holding capacity) (incubation experiments). The temperature sensitivity of soil microbial respiration rate (Q10) varied from 1.76 to 2.25 for the non-incubated soils and was similar to the incubated soils, which ranged from 1.77 to 2.43. In the non-incubation experiments, the greatest dissolved organic carbon (DOC) values (0.57 mg g− 1) occurred in the soils with moderate soil moisture, then followed by the wet soils (0.31 mg g− 1), and lastly (0.18 mg g− 1) by the dry soils; in the incubation experiment, the DOC was significantly (P < 0.05) greater at 10 °C (0.28 mg g− 1) than that incubated at 30 °C (0.20 mg g− 1). The regression results showed that the soil water-soluble carbon content was the main factor that had a significant (P < 0.01) influence on the temperature sensitivity of soil microbial respiration in both experiments. It is concluded that substrate availability controls temperature sensitivity of soil microbial respiration in the grassland soils. The variations of the Q10 and its dependence on substrate availability have important implications for regional and global ecosystem carbon modeling, specifically in predicting the response of terrestrial ecosystems to future global warming.