Revegetation has been proposed as an effective approach to restoring the extremely degraded grassland in the Qinghai-Tibetan Plateau (QTP). However, little is known about the effect of revegetation on ecosystem carbon density (ECD), especially in alpine permafrost regions. We compared aboveground biomass carbon density (ABCD), belowground biomass carbon density (BBCD), soil organic carbon density (SOCD), and ECD in intact alpine meadow, extremely degraded, and revegetated grasslands, as well as their influencing factors. Our results indicated that (1) ABCD, BBCD, SOCD, and ECD were significantly lower in extremely degraded grassland than in intact alpine meadow; (2) ABCD, SOCD, and ECD in revegetated grassland significantly increased by 93.46%, 16.88%, and 19.22%, respectively; (3) stepwise regression indicated that BBCD was mainly influenced by soil special gravity, and SOCD and ECD were controlled by freeze-thaw strength and soil temperature, respectively. This study provides a comprehensive survey of ECD and basic data for assessing ecosystem service functions in revegetated grassland of the alpine permafrost regions in the QTP.

The impact of climate change in the European Alps has been roughly twice the global average, dramatically reducing permafrost extent and thickening of its active layer. Therefore, the study of the abiotic factors (i.e. chemical/physical parameters) affecting the microbial diversity inhabiting Alpine permafrost appears to be of dramatic relevance. Within the European Alps, the Stelvio area exhibits these effects in a particularly evident way, with important consequences on microbial ecosystems. Therefore, microbial communities inhabiting a permafrost core collected in the Scorluzzo active rock glacier (Stelvio Pass, Italian Central Alps) were investigated along a depth gradient (410 to 524 cm from the surface). The taxonomic structures of bacterial and fungal communities were investigated via a next-generation sequencing (NGS) approach (Illumina MiSeq), targeting the bacterial V3-V4 regions of 16S rDNA and the fungal ITS2 region. Abiotic soil factors (grain size, electrical conductivity, ice/water content, pH, Loss-on-Ignition - LOI, total and organic carbon, nitrogen and phosphorous) were analysed. Richness and Shannon-H diversity indices were correlated to abiotic factors. Bacterial diversity was significantly (p < 0.05) correlated with LOI, while fungal diversity was significantly (p < 0.05) correlated with the depth gradient. The Constrained Analysis of Principal (CAP) coordinates were used to study the correlation between abiotic parameters and the taxonomic structure of bacterial and fungal communities. Among all tested variables, the depth gradient, water content, pH and LOI affected the taxonomic structure of bacterial communities (in particular, the abundance of bacterial amplicon sequence variants - ASVs - assigned to Afipia sp., Chloroflexi, Gaiella sp., Oryzihumus sp. and Serratia, sp.), while fungal communities (ASVs assigned to Naganishia sp., Rhodotorula sp., Sordariomycetes and Taphrinales) were affected by the depth gradient. Co-occurrences (calculated by Pearson correlation coefficient) among microbial taxa (i.e. bacteria vs bacteria, bacteria vs fungi, fungi vs fungi) were investigated: the prevalence of significant (p < 0.05) positive co-occurrences was found, suggesting that the coexistence of different microbial taxa could play a crucial role in maintaining the ecological and taxonomic balance of both bacterial and fungal communities inhabiting the Alpine permafrost ecosystem. These findings suggest that the bacterial and fungal diversity of Alpine permafrost are affected in different ways by some abiotic factors.

Thermokarst depressions are widespread phenomena due to permafrost degradation in the Arctic, whereas only few are known from mountain permafrost of the mid-latitudes. In the Italian Central Alps, close to the Stelvio Pass (2,763 m above sea level), a ski run was built in 1987. Since 1981, statistically significant air warming has been recorded, especially during summer (+0.65 degrees C per decade). Permafrost temperature recorded at the nearby Share Stelvio Borehole between 1990 and 2011 exhibited a rapid increase (> 0.8 degrees C per decade) and an active-layer thickening (7 cm/year). Between the years 1999 and 2003, some thermokarst depressions started to develop, initially in the lower part of the ski run and then extending to higher elevations. The depressions increased in number, size, and depth with time. Since ski-run construction, the area remained free of vegetation until early 2000, when vegetation colonization started, showing a coupling with the onset of thermokarst development and summer warming. Vegetation changes accelerated with the ingress of pioneer and early-successional as well as of late-successional species. Moreover, the ingress of shrub species (Salix spp.) typical of lower elevation belts (subalpine and even montane) was dated to 2004. All the observed features show a rapid and coupled response of the abiotic and biotic components of this ecosystem to climate warming. Our data also confirm the similarity of the observed responses and dynamics of the alpine tundra with the Arctic tundra with regard to both permafrost and vegetation.

It is generally believed that there is a vegetation succession sequence from alpine marsh meadow to desert in the alpine ecosystem of the Qinghai-Tibet Plateau. However, we still have a limited understanding about distribution patterns and community assemblies of microorganisms' response to such vegetation changes. Hence, across a gradient represented by three types of alpine vegetation from swamp meadow to meadow to steppe, the soil bacterial, fungal and archaeal diversity was evaluated and then associated with their assembly processes, and glacier foreland vegetation was also surveyed as a case out of this gradient. Vegetation biomass was found to decrease significantly along the vegetation gradient. In contrast to irregular shifts in alpha diversity, bacterial and fungal beta diversities that were dominated by species replacement components (71.07-9.08%) significantly increased with the decreasing gradient in vegetation biomass (P < 0.05). These trends of increase were also found in the extent of stochastic bacterial and fungal assembly. Moreover, an increase in microbial beta diversity but a decrease in beta nearest taxon index were observed along with increased discrepancy in vegetation biomass (P < 0.001). Stepwise regression analyses and structural equation models suggested that vegetation biomass was the major variable that was related to microbial distribution and community assembly, and there might be associations between the dominance of species replacements and stochastic assembly. These findings enhanced our recognition of the relationship between vegetation and soil microorganisms and would facilitate the development of vegetation-microbe feedback models in alpine ecosystems.

The Tien Shan Mountains, the largest mountain range in the Xinjiang Autonomous Region of north-western China, significantly influence the climate of central Asia. Recent permafrost changes in the region of the headwaters of the Urumqi River, as well as its relationship to climatic factors, were studied based on ground temperatures measured in a 60 m deep borehole, air temperatures and precipitation over a period from 1992 to 2011. The results showed that the maximum active-layer thickness (ALT; 1.70 m) occurred in 2009 and 2011, with an increase of 0.45 m compared with 1992. The change in ALT was related to the variation in the climatic conditions, and the increase in the deep-seated permafrost temperature. The permafrost temperature increased from -1.7 degrees C in 1992 to -1.1 degrees C in 2011, and the permafrost base moved upwards by approximately 14 m from 1992 to 2011. The long-term step-wise change in the air temperature may be the main cause of the permafrost warming in the headwaters of the Urumqi River. Copyright (c) 2015 John Wiley & Sons, Ltd.