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.

Though one of the most vulnerable terrestrial ecosystems, wetlands provide multiple ecosystem services, most notably storing carbon. It is now widely recognized that climate change could have a large impact on high-latitude wetlands. A key question is how climate change will affect the distribution pattern of wetland plant communities, and to what extent the transitions among different wetland plant communities respond to regional warming? To answer this question, we estimated the total SOC storage with 139 soil profiles in the Xing'anling Mountains and performed ensemble species distribution modelling for 11 dominant wetland plant communities by using numerous vegetation plots. Results show that 4.5-23.8% of the high-latitude wetlands in the study area would be lost following widespread thawing of permafrost under different climate warming scenarios by the end of this century. The total wetland SOC in the Xing'anling Mountains is estimated to be 1.58 Pg, about 25.5-29.3% of the total of China's wetlands, however, predicted wetland loss could put 5.4-20.5% (0.08-0.32 Pg C) of the total SOC storage at risk of instability. Our results also predicted a significant northward migration of southern Deyeuxia angustifolia communities driven by future climate changes. This wetland succession could profoundly reduce future carbon sequestration capacity of wetlands in the study area. The findings presented here are helpful for both current reserve management and future conservation planning of wetlands in the study area.