Alpine grasslands are vital in regulating carbon balance on the Qinghai-Tibetan Plateau (QTP) because of the large soil organic carbon (SOC) stocks, while persistent disturbance from the endemic small semifossorial herbivore, plateau pika (Ochotona curzoniae, hereafter pika), may break this balance. Pika affect the soil microclimate by creating a heterogeneous underlying surface, which is expected to alter soil microbial communities and eventually SOC stocks. However, our knowledge regarding the potential influence mechanism is still limited. Here, we investigated vegetation biomass, soil properties and soil microbes among 4 different surfaces (i.e., original vegetation, new pika pile, old pika pile and bare patch) of typical alpine grasslands to reveal soil microbial communities and the associated effect on SOC in response to pika bioturbation. Our results showed that pika bioturbation increased both bacterial and fungal diversity and their phyla abundance for SOC decomposition. Vegetation biomass, electrical conductivity and NH4+-N accounted for the variation in both bacterial and fungal community compositions and diversity. SOC stocks were 15-30% lower in pika piles and bare patches than in the original vegetation, which was mainly attributed to the reduced soil organic matter input from vegetation and the enhanced SOC consumption by soil microbial communities. Overall, we conclude that pika bioturbation altered the diversity and composition of soil microbial communities, which was associated with SOC loss and positive carbon feedback in alpine grasslands. Our findings provide insights into the role of small semifossorial herbivores in the carbon cycle of global grasslands.

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg ‧ha  1 ‧a  1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

All ecosystems face ecological challenges in this century. Therefore, it is becoming increasingly important to understand the ecology and degree of local adaptation of functionally important Arctic-alpine biomes by looking at the most diverse taxon of metazoans: the Arthropoda. This is the first study to utilize metabarcoding in the Alpine tundra, providing insights into the effects of micro-environmental parameters on alpha- and beta-diversity of arthropods in such unique environments. To characterize arthropod diversity, pitfall traps were set at three middle-alpine sampling sites in the Scandinavian mountain range in Norway during the snow-free season in 2015. A metabarcoding approach was then used to determine the small-scale biodiversity patterns of arthropods in the Alpine tundra. All DNA was extracted directly from the preservative EtOH from 27 pitfall traps. In order to identify the controlling environmental conditions, all sampling locations were equipped with automatic data loggers for permanent measurement of the microenvironmental conditions. The variables measured were: air temperature [degrees C] at 15 cm height, soil temperature [degrees C] at 15 cm depth, and soil moisture [vol.%] at 15 cm depth. A total of 233 Arthropoda OTUs were identified. The number of unique OTUs found per sampling location (ridge, south-facing slope, and depression) was generally higher than the OTUs shared between the sampling locations, demonstrating that niche features greatly impact arthropod community structure. Our findings emphasize the fine-scale heterogeneity of arctic-alpine ecosystems and provide evidence for trait-based and niche-driven adaptation. The spatial and temporal differences in arthropod diversity were best explained by soil moisture and soil temperature at the respective locations. Furthermore, our results show that arthropod diversity is underestimated in alpine-tundra ecosystems using classical approaches and highlight the importance of integrating long-term functional environmental data and modern taxonomic techniques into biodiversity research to expand our ecological understanding of fine- and meso-scale biogeographical patterns. Our study examines the alpha- and beta-diversity of arthropods in the Arctic-alpine biomes of the Scandes using environmental DNA (eDNA)/metabarcoding. We found that micro-climatological parameters such as air/soil temperature and soil moisture significantly influence the arthropod community structure, highlighting the fine-scale heterogeneity of these ecosystems. Our study emphasizes the importance of integrating long-term functional environmental data and modern taxonomic techniques to accurately assess arthropod diversity and broaden our understanding of biogeographical patterns in alpine-tundra ecosystems.image

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg ‧ha  1 ‧a  1 during 2001-2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Alpine vegetation plays an important role in the thermal stability of the permafrost under a warming climate, as it affects ground hydrothermal dynamics. The response of soil hydrothermal dynamics in the active layer to permafrost degradation under different alpine grassland types is unclear on the Qinghai-Tibet Plateau. In this study, long-term soil temperature and soil water content in the active layer were monitored in situ from October 2010 to December 2018 at five sites in the Kaixinling permafrost region on the interior Qinghai-Tibet Plateau along the Qinghai-Tibet Railway. The sites included an alpine steppe (AS), three alpine meadows (AM) with different degrees of degraded vegetation, and an alpine swamp meadow (ASM). Based on field-monitored data, the variations in soil temperature, soil water content, and freeze-thaw processes were examined in the active layer. The response characteristics of the soil hydrothermal processes to climate change were analysed under the different alpine grasslands. The results showed that the duration of the thawing and freezing stages of the active layer of the AMs was shorter than that of the ASM and the AS. The average mean annual soil temperature (MAST) in the active layer of the AM ((-1.25 & PLUSMN; 0.50) & DEG;C) was lower than those in the AS ((-0.71 & PLUSMN; 0.39) & DEG;C) and ASM ((-0.45 & PLUSMN; 0.57) & DEG;C), while the AM had the highest rate of soil temperature increase ((0.2 & PLUSMN; 0.06) & DEG;C per year). The annual amplitude of ground temperature in the active layer increased with the transition direction of the alpine vegetation type from ASM to AM to AS. The small surface offset (SO) and thermal offset (TO) (absolute values) indicated that the ground thermal state of the AM was more unstable, as it was more sensitive to the increase in air temperature than the ASM or the AS. Soil properties controlled the distribution of soil water content within the active layer, but vegetation improved the shallow soil structure by producing more belowground phytomass, thus, enhancing soil water content in the 0-30 cm layer. The average soil water content at depths of 0-30 cm was directly proportional ( p < 0.05) to the phytomass. Soil water contents at depths of 0-30 cm in the ASM ((37.7 & PLUSMN; 5.3)%) and the AM ((40.8 & PLUSMN; 5.9)%) were significantly higher than those in the AS ((22.7 & PLUSMN; 3.2)%). These results provide valuable insight into the hydrothermal interactions between the degradation of permafrost and alpine vegetation under a warming climate.

Alpine ecosystems play an important role in maintaining carbon sequestration, water balance, ecological security, biodiversity and human well-being. However, climate change and high-intensity human activities lead to the continuous degradation of vulnerable alpine ecosystems. Based on this, we reveal trends in ecosystem change in the Qilian Mountains of China on a 40-year scale and identify the primary driving factors of change in alpine ecosystems from the perspective of ecosystem service value (ESV) change, providing a more comprehensive picture of the interactions between human society and natural ecosystem. The results showed that more than 55 % of ecosystem types changed from 1980 to 2018, with forests, grasslands, glaciers and bare land being the most vulnerable ecosystems to disturbance, and forest and grassland ecosystems having significant ESV potential (43.99 % and 29.57 %, respectively). However, significant land use and land cover (LULC) changes over the last decade have led to a reduction in ESV stability in alpine ecosystems, where human activities have a more significant impact on ESV of sparse woodland, shrubland and grassland ecosystem at 2800-4000 m. The temperature rise had a more noticeable impact on the ESV of glaciers, alpine meadows and bare land ecosystems at 4000-5500 m. In the long terms, climate change and population growth will threaten the restoration and management of alpine ecosystems. Different ecological development strategies need to be adopted along the altitude, and the establishment of cross regional horizontal ecological compensation mechanism should be accelerated to promote the sustainable development of ecology and people's livelihood in mountainous areas. The results of this study will provide relevant theoretical basis and reference for decision makers, and provide a model for scientific management and sustainable development of alpine ecosystem resources worldwide.

Continuing permafrost degradation is increasing the risk of mercury (Hg) exposure in the permafrost regions on the Qinghai-Tibetan Plateau (QTP), but related studies are still limited, especially the ones on the detailed Hg migration processes in permafrost. The vertical distribution characteristics of soil Hg were investigated in three ecosystems in the Beiluhe area on the QTP, and its influencing factors and formation mechanism were investigated. The results indicate that the total soil mercury (THg) concentration in the Beiluhe area remains at an extremely low level (6.33 +/- 2.45 ng/g). In the vertical profile, the THg concentration of the shallow soil layer (0-50 cm) (5.96 +/- 2.22 ng/g) is significantly lower than that of the deep layer (50-400 cm) (7.44 +/- 2.71 ng/g) ( p < 0.05). Within the upper 50 cm, the THg concentration decreases with soil depth, and the peak THg concentration occurs at 100-300 cm on the entire profile. Although the THg concentration is slightly affected by the organic matter in the shallow soil layer, in general, the soil parent material is the dominant factor affecting the THg concentration. Intense weathering results in a low THg concentration in the shallow soil layer because the soil Hg is carried downward with the soil moisture. To a certain depth, the impermeable frozen soil layer intercepts the flow of the soil Hg, and it forms a Hg enrichment layer. This paper presents the distinctive pattern of the soil Hg distribution in the permafrost regions of the QTP. (c) 2021 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

Rapid warming in alpine regions exerts important effects on carbon cycling in alpine ecosystem, which are sensitive to environmental changes. So far, little is known about the spatial and temporal variation in carbon budgets and the main influencing factors over different ecosystems. Here, we examined the monthly and annual gross primary production (GPP), net ecosystem CO2 exchange (NEE) and ecosystem respiration (ER) during 2004-2017 in four types of ecosystems (i.e., alpine meadow, steppe, forest and cropland) on the Tibetan Plateau. We explored the relationships between carbon fluxes and environmental factors. The results show that forest, cropland and alpine meadow ecosystems acted as carbon sinks, with NEE values ranging from -21.25 +/- 3.54 to -308.75 +/- 21.65 g C m-2a-1, while alpine steppe and overmature forest ecosystems serve as carbon sources (mean annual NEE: 23.12 +/- 15.88 g C m-2a-1). The temperature sensitivity values (Q10) of ER in the forest (9.39) and alpine steppe (7.47) ecosystems were greater than those in the alpine meadow ecosystems (Q10 = 4.20), indicating that the carbon emissions in the forest and alpine steppe ecosystems were more sensitive to warming. Multiple linear regression analysis indicated that the carbon fluxes (GPP, NEE, ER) of alpine steppe and alpine meadow in the permafrost regions were more sensitive to water forcing (precipitation, soil water content), while in the forest and cropland ecosystems temperature forcing (air and soil temperature) were strong predictors of all the carbon flux indices. Our results showed differential responses of carbon budgets among ecosystems, which could be considered in the future modeling of carbon cycle in alpine regions.

Soil moisture plays a vital role in regulating the direction and magnitude of methane (CH4) fluxes. However, it remains unclear whether the responses of CH4 fluxes to climate warming exhibit difference between dry and moist ecosystems. Based on standardized manipulative experiments (i.e., consistent experimental design and measurement protocols), here we explored warming effects on growing season CH4 fluxes in two alpine grasslands with contrasting water status on the Tibetan Plateau. We observed that experimental warming enhanced CH4 uptake in the relatively arid alpine steppe, but had no significant effects on CH4 emission in the moist swamp meadow. The distinct responses of CH4 fluxes were associated with the different warming effects on biotic and abiotic factors related to CH4 oxidation and production processes. Warming decreased soil water-filled pore space (WFPS) and increased the pmoA gene abundance and CH4 oxidation potential in the alpine steppe, which together led to a significant increase in CH4 uptake at this alpine steppe site. However, warming-induced enhancement in CH4 oxidation potential might be counteracted by the simultaneously increased CH4 production potential in the swamp meadow, which could then result in insignificant warming effects on CH4 emission at this swamp meadow site. Based on a meta-analysis of warming effects on CH4 fluxes across the entire Tibetan Plateau, we found that the entire alpine grasslands could absorb an extra 0.042 Tg CH4 (1 Tg = 10(12) g) per growing season if soil temperature increased by 1 degrees C. These findings demonstrate that warming effects on CH4 fluxes differ between two alpine grasslands with contrasting moisture conditions and the entire alpine grasslands may not trigger a positive CH4 feedback to climate system with moderate warming.

High-latitude and high-altitude ecosystems store large amounts of carbon (C) and play a vital role in the global C cycle. Soil respiration (R-S) in these ecosystems is believed to be extremely sensitive to climate warming and could potentially trigger positive C-climate feedback. However, this evidence is largely derived from wet ecosystems, with limited observations from dry ecosystems. Here, we explored the responses of R-S, autotrophic (R-A), and heterotrophic (R-H) respiration under experimental warming in a dry ecosystem, an alpine steppe on the Tibetan Plateau. We assessed the effects of soil temperature and moisture dynamics on R-S, R-A, and R-H and performed a meta-analysis to examine whether the warming effects observed were similar to those reported in wet ecosystems, including Tibetan alpine meadow and arctic ecosystem. Experimental warming did not alter R-S, R-A, and R-H in this alpine steppe, likely because decreased soil moisture constrained positive warming effects. In contrast, the meta-analysis revealed that R-S exhibited a significant increase under experimental warming in both the Tibetan alpine meadow and arctic wet tundra. These results demonstrate that R-S exhibits different responses to climate warming between dry and wet ecosystems, suggesting potential more complex C-climate feedback in cold regions.