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Warming in mountain regions is projected to be three times faster than the global average. Pronounced climate change will likely lead to species reshuffling in mountain plant communities and consequently change ecosystem resilience and functioning. Yet, little is known about the role of inter‐ versus intraspecific changes of plant traits and their consequences for functional richness and evenness of mountain plant communities under climate change. We performed a downslope translocation experiment of intact plant‐soil mesocosms from an alpine pasture and a subalpine grassland in the Swiss and Austrian Alps to simulate an abrupt shift in climate and removal of dispersal barriers. Translocated plant communities experienced warmer and dryer climatic conditions. We found a considerable shift from resource conservative to resource acquisitive leaf‐economy in the two climate change scenarios. However, shifts in leaf‐economy were mainly attributable to species turnover, namely colonization by novel lowland species with trait expressions for a wider range of resource use. We also found an increase in vegetative height of the warmed and drought‐affected alpine plant community, while trait plasticity to warming and drought was limited to few graminoid species of the subalpine plant community. Our results highlight the contrast between the strong competitive potential of novel lowland species in quickly occupying available niche space and native species' lack of both the intraspecific trait variability and the plant functional trait expressions needed to increase functional richness under warming and drought. This is particularly important for the trailing range of many mountain species (i.e. subalpine zone) where upward moving lowland species are becoming more abundant and abiotic climate stressors are likely to become more frequent in the near future. Our study emphasizes mountain plant communities' vulnerability to novel climates and biotic interactions under climate change and highlights graminoid species as potential winners of a warmer and dryer future. Keywords: alpine grassland, functional diversity, invasion, species turnover, traitspace, translocation [ABSTRACT FROM AUTHOR]

• Intact plant-soil mesocosms are translocated along an elevational gradient ranging from 1260 m to 350 m a.s.l. • Translocated microorganisms increased their active fraction, enzymatic activity and changed enzyme systems. • Warming in combination with decreased precipitation leads to shifts in microbial life strategies to K -strategists. • Microorganisms are C limited along the translocation from higher to lower elevations. • Climate change with warmer temperatures and periodically less precipitation will modify the microbial C and N demand. Soil microorganisms are the major players controlling the soil carbon (C) and nutrient cycling, however the extent to which the functional properties of soil microorganisms will alter with climate change in mountain grasslands is still unclear. To simulate future climatic conditions (higher temperature and less precipitation), intact plant-soil mesocosms of three mountain grassland sites, Esterberg (1260 m a.s.l.), Graswang (860 m a.s.l.), and Fendt 550 m a.s.l.), were translocated to the lowest elevation Bayreuth (350 m a.s.l.). After two years of translocation to warmer and drier environments, specific growth rates of soil microorganisms were 25 % slower than those at higher elevations. This indicated a shift towards to slow-growing K -strategists with increasing temperature and decreasing soil moisture, presumably attributed to the depletion of available C for microorganisms. Simultaneously, higher activity and faster substrate turnover time of C-acquiring enzymes in the warmer and drier soils implied a stronger C rather nutrient limitation. This was supported by the increased vector length, which was induced by decreased dissolved organic compounds at lower elevation. In contrast, microorganisms were limited by nitrogen (N) at higher elevation because of the stronger competition for N between plants and microorganisms. In short, translocated microorganisms increased their active fraction, enzymatic activity and altered enzyme systems but decreased specific growth rates. This indicated that soil microbial community adjusted to the changing climate resulting in faster substrate turnover, and in turn caused 15 % reduction in soil C content from Esterberg to Bayreuth. We therefore conclude that climate warming in combination with decreased precipitation increases microbial activity, leads to shifts in microbial life strategies and induces alterations in microbial nutrient limitation, i.e. shift from N- to C and P co-limitation with translocation to lower elevation sites. This in turn, is likely to result in C losses of mountain grassland soils under future climate change, which will amplify negative impacts on global warming. [ABSTRACT FROM AUTHOR]

• Simulated warming caused a rapid loss of OC in mountainous grassland soils rich in OM. • SOC loss was associated with a disruption of large-macroaggregates. • Intensive grassland slightly offset OC losses and promoted SM formation. • Soil perturbation effects have to be differentiated from climate change effects. Mountainous grassland soils are considered one of the most unique biological hotspots, rich in organic carbon (OC). At the same time, they are exposed to great threats, as climate warming is more pronounced in mountainous regions than in lowland areas. In this study, we assessed the effect of simulated warming (+1K, +2K, and + 3 K) on OC stocks and soil structure in grassland soils of the Northern Limestone Alps in Germany by translocating plant-soil mesocosms from high- (1260 m a.s.l., Rendzic Phaeozem) and mid- (860 m a. s. l., Haplic Cambisol) to low-elevation (600 m a.s.l). Plant-soil mesocosms were exposed to both extensive and intensive grassland management practices. Four years after translocation, we observed a rapid decrease of topsoil SOC stocks under intensive (−1.0 t C ha yr−1) and extensive management (-2.2 t C ha yr−1), under the highest temperature increase. Intensive management with about 1 t C ha−1 yr−1 higher manure C return than extensive management (1.6 vs. 0.8 t C ha−1 yr−1 intensive and extensive, respectively) may explain the difference in SOC losses between different management treatments. Under both management practices, the loss of SOC was mainly associated with a decrease of large macroaggregates, at both management practices. In addition, different aggregate specific OC loss rates resulted in an altered distribution of OC among the aggregate size classes. Our study provides evidence that simulated climate change induced a rapid and substantial decline of SOC in mountainous, OC-rich grassland soils, which may be attributed to decreased physical OC protection within large macroaggregates. Optimized grassland management in form of increased application of organic fertilizers could only partially offset the SOC loss by improved formation of small macroaggregates. [ABSTRACT FROM AUTHOR]