Temperature sensitivity of soil microbial respiration in soils with lower substrate availability is enhanced more by labile carbon input

The temperature sensitivity (O-10) of soil microbial respiration (R-s) is a critical parameter for predicting soil carbon (C) fluxes under changing climatic conditions, and labile C is continuously input into soil via root exudates or plant litter in field. However, how Q(10) responds to labile C input remains uncertain, especially across large geographical regions. We collected eight soils from tropical to cold-temperate forests along a north-south transect in eastern China, and soils were added with either water as a control or glucose as an analogue for labile C input to investigate how Q(10) responds to labile C input at a large geographical scale. Then, soils were incubated under varying temperature conditions from 5 to 30 degrees C for 2-weeks, and R-s was measured at a high frequency (each sample was measured at 20 min intervals within 12 h) after 1 d, 7 d and 14 d incubation. R-s and Q(10) were then calculated for both the control and glucose addition treatments. Compared with those in the control, glucose addition significantly increased R-s and Q(10) in all forest soils. The increase in Q(10) (Delta Q(10)) between the control and glucose addition treatments differed significantly among the eight forest soils and was the highest in mid-latitude regions. Furthermore, Q(10) was significantly and negatively correlated with the soil C availability index (CAI), indicating that the Q(10) of soils with lower basal substrate availability (e.g., soils in mid-latitudes of eastern China) are enhanced more by labile C input than those of higher basal substrate availability. A significant negative relationship between Q(10) and substrate quality (SQI, measured as basal microbial respiration rate at 0 degrees C) without glucose addition supported the carbon quality temperature hypothesis; however, this hypothesis was not always valid after adding glucose. Our findings highlight the importance of basal substrate availability in influencing Q(10) after labile C addition, suggesting that C-climate models should incorporate different scenarios of labile C input in the future.

Automated summary

The addition of labile carbon significantly increased soil microbial respiration rate and temperature sensitivity at a large geographical scale, particularly in mid-latitude regions. Q(10) was significantly negatively correlated with the soil carbon availability index, suggesting that basal substrate availability has a strong influence on Q(10) after labile carbon addition.