| Summary: | Rising air temperatures caused by global warming affects microbial decomposition rate of soil organic matter (SOM). The temperature sensitivity of SOM decomposition (Q<sub>10</sub>) may depend on SOM quality determined by vegetation type. In this study, we selected a long transect (3.6 km) across the five ecosystems and short transects (0.1 km) from grazed and ungrazed meadows to forests in the Northwest Caucasus to consider different patterns in Q<sub>10</sub> changes at shift of the vegetation belts. It is hypothesized that Q<sub>10</sub> will increase along altitudinal gradient in line with recalcitrance of SOM according to kinetics-based theory. The indicators of SOM quality (BR:C, respiration per unit of soil C; MBC:C, ratio of microbial biomass carbon to soil carbon; soil C:N ratio) were used for checking the hypothesis. It was shown that Q<sub>10</sub> did not differ across vegetation types within long and short transects, regardless differences in projective cover (14–99%) and vegetation species richness (6–12 units per plot). However, Q<sub>10</sub> value differed between the long and short transects by almost two times (on average 2.4 vs. 1.4). Such a difference was explained by environmental characteristics linked with terrain position (slope steepness, microclimate, and land forms). The Q<sub>10</sub> changes across studied slopes were driven by BR:C for meadows (R<sup>2</sup> = 0.64; negative relationship) and pH value for forests (R<sup>2</sup> = 0.80; positive relationship). Thus, proxy of SOM quality explained Q<sub>10</sub> variability only across mountain meadows, whereas for forests, soil acidity was the main driver of microbial activity.
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