Results
During the four weeks incubation, daily microbial respiration rates at the incubation temperature (MR) and adjusted at the field MAT (MR_MAT), base respiration at 0 ℃ (MR_0), and their normalizations by soil C concentration were all were all declining over time in all elevational gradients. While, there was no significant temporal trend ofQ 10 over the four weeks (Fig. S1-S2).
Four-week accumulated MR at incubated temperature (AccMR) and base respiration at 0 ℃ (AccMR_0) increased as elevation increased, while the adjust accumulated MR at the field MAT (AccMR_MAT) andQ 10 did not vary significant along with the elevation. The normalized AccMR_MAT and AccMR_0 by soil C concentration (AccMR_MAT_perSC and AccMR_0_perSC) both decreased nonlinearly as elevation increased (Fig. 1, S3-S6).
In the selected model for each group of factors (Fig. S7-S12), AccMR_MAT was positively affected by pH and WHC in the soil environment factors, Root P concentration and Root NPR in the carbon input factors, soil available N and NPR in soil organic matter factors, negatively affected by Actinomyces in soil microbial factors. In total, soil organic matter explained the largest variation of AccMR_MAT (0.24), followed by soil environment (0.13) and soil microbial community (0.10, Figure 2a).
Q 10 was positively affected by fine root biomass in carbon input factors, negatively affected by litter N concentration in carbon input factors. In total, carbon input factors explained the largest variation of Q 10 (0.13, Figure 2b).
SEM analysis showed that 71% variation of AccMR_MAT was explained by the investigated abiotic and biotic factors (Figure 3a). The majority of this explanation was directly contributed by the positive effects of soil pH, AccMR_0_perSC and WHC, with standardized effects of 0.63, 0.54 and 0.51, respectively (Figure 4a). We further found that soil microbial C caused key indirect effect on AccMR_MAT. Moreover, MAT, aspect and MAP also caused significant positive effect on the variation of AccMR_MAT, with standardized total effects of 0.27, 0.10 and 0.09, respectively; while elevational gradients caused significant negative effect on AccMR_MAT, with standardized total effect of -0.16 (Figure 4a).
Variation of Q 10 in the SEM was explained 38%, which was contributed by the directly negative effect from AccMR_0_perSC, elevation and litter N concentration, with standardized effects of -0.62, -0.43 and -0.28, respectively (Figure 3b). In total, we further found that WHC, Aspect, fine root biomass, MAP and microbial NPR caused indirectly positive effect on Q 10, all via MR_0_perSC (Figure 4b).