Elevational variation and drivers of soil microbial respiration
In this study, the incubated AccMR increased along with the elevation. This phenomenon is similar to other incubation studies (Kong et al. , 2022), but opposite to the field measurements that soil respiration declines from low to high elevation (Garten and Hanson, 2006; Gutiérrez-Girón et al. , 2015). In the lab measurement, since all soil samples were incubated at the same temperature, high AccMR at high elevation was largely contributed by its high soil C concentration and microbial biomass C (Figs. S10-S11). However, field temperature is declining from low to high elevation (Fig. S7). After adjust by the field MAT, no significant elevational trend of AccMR_MAT was examined, because the low MAT of sampled high elevation limits microbial activity, thus, offsetting the positive effect from high SOC concentration. However, most previous incubation studies used a unify temperature (or temperature range) no matter where soil was sampled, the unified incubation temperature is relatively high to cold site samples and potentially overestimates their soil C release, relatively low to the warm site samples and potentially underestimates their soil C release (Li et al. , 2020; Zhang et al. , 2022). Future incubation experiment should pay more attention on this uncertainty, by using different incubating temperature or at least adjusting the C release by the natural temperature gradients of each sampling site (Liet al. , 2020).
In this study, the declining AccMR_MAT from low to high elevation was dominantly contributed by soil environments (pH and WHC) and soil C quality (AccMR_0_perSC), followed by soil microbial biomass C, MAT, aspect and MAP. The dominant factors were similar to previous studies that soil micro-environments (Ding et al. , 2016; Li et al. , 2020; Zhang et al. , 2022) and initial quality of soil C (Guo et al. , 2022) played critical role in regulating microbial respiration. While our results were differ to other studies that suggests the critical role of soil microbe in determining soil C decomposition (Colman and Schimel, 2013). Possible explanation is that soil microbe is highly collinear with soil pH and WHC, the influence of soil microbe was implied in the effect of soil pH and WHC. These results suggest that soil environment and soil C quality are much important in determining soil C decomposition.