Extracellular enzyme characteristics and microbial metabolic limitation in soil of subalpine forest ecosystems on the eastern Qinghai-Tibetan Plateau

Aims: Subalpine forest ecosystems are sensitive to climate change, and extracellular enzyme activities and microbial metabolic limitation in soils are influenced by multiple factors including climate. The study aims to reveal the extracellular enzyme characteristics and microbial metabolic limitation in soils and their key drivers along an elevation gradient in subalpine forest ecosystems. Methods: Microbial metabolic limitations in bulk and rhizosphere soils under Quercus aquifolioides forest along an elevation gradient (3100-4180 m a.s.l) of Pamuling Mountain on the eastern Qinghai-Tibetan Plateau were investigated by enzyme stoichiometry theory and path modelling analysis. Results: Elevation had significant effects on the carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring enzyme activities, but the difference between bulk and rhizosphere soil was non-significant. Microbial metabolism was mainly limited by C and P, and showed a tendency to gradual shift from C and P limitation to C and N limitation at high elevation. The C limitation of microbial metabolism showed an increasing trend with elevation, implying greater C limitation at higher elevations where temperatures were lower. Therefore, we infer that the increase in temperature may help to alleviate C limitation of microbial metabolism in subalpine forest. Soil available nutrients affected N and P limitations of microbial metabolism, and soil pH, nutrient ratios and available nutrients mainly affected C limitation. Conclusions: There were significant influences of elevation on soil enzyme activities and C limitation of microbial metabolism. Soil pH, nutrient stoichiometric characteristics and available nutrients were the key factors affecting soil microbial metabolism in subalpine Q. aquifolioides forest ecosystems.