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).