Soil incubation and measurements
We performed the lab incubation experiment under varying temperature to quantify the MR and Q 10 of the 45 soil samples. The incubation and measurement were conducted using a 32-channel microbial respiration automatic measurement system in lab. For detail about this measurement system, please refer to (Zhang et al. , 2022).
Before measurement, all soil samples were adjusted to 60% WHC to maximum soil microbial activity (Zhou et al. , 2014). 40 gram dry-weight soil for each soil sample was placed in a bottle (250 ml) for incubation. The measurement last 4-weeks after one-week pre-incubation. During the pre-incubation and measurement, the artificial weather box experienced the same temperature cycle every day, i.e., 10 oC-15oC-20 oC-25 oC-20oC-15 oC-10 oC. All soil samples were maintained with 60% water holding capacity by weekly weighing the soil containers and adding distilled water to compensate for water loss. Each temperature last 240-minute, in which the former 80-minute was equilibration time and the latter 160-minute was for measurement. Each measurement lasts 150 s, with the 60th-140th s data for determining the soil C decomposition rate. The rate of soil C decomposition at different temperature was used to calculate the daily accumulated MR andQ 10 following Eq-1 (Lloyd and Taylor, 1994).
MR=aebT (1)
where MR was the rate of soil C decomposition at specific incubated temperature, T was the incubated temperature, arepresent the base respiration at T =0 ℃ for each soil sample (MR_0). b was parameter of the exponential equation and used to calculate Q 10 value, following Eq. (2)
Q 10=e 10b (2)
MR at each specific field temperature was calculated following:
MR_MAT=aebT_MAT (3)
Where MR_MAT is MR at the specific field mean annual temperature (MAT) at each plot, and T_MAT is the field MAT at each plot.
For the four weeks incubation, we calculated the accumulated microbial respiration, such as AccMR for the incubated respiration, AccMR_0 for the base respiration at T =0 ℃, AccMR_MAT for the adjusted respiration. AccMR_0 was further normalized by soil C concentration (AccMR_0_perSC) to represent the quality of soil C substrate (Creameret al. , 2014; Ding et al. , 2016).