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High-altitude and alpine areas are predicted to experience rapid and substantial increases in future temperature, which may have serious impacts on soil carbon, nutrient and soil fauna. Here we report the impact of 20 years of experimental warming on soil properties and soil mites in three contrasting plant communities in alpine/subarctic Sweden. Long-term warming decreased juvenile oribatid mite density, but had no effect on adult oribatids density, total mite density, any major mite group or the most common species. Long-term warming also caused loss of nitrogen, carbon and moisture from the mineral soil layer in mesic meadow, but not in wet meadow or heath or from the organic soil layer. There was a significant site effect on the density of one mite species, Oppiella neerlandica, and all soil parameters. A significant plot-scale impact on mites suggests that small-scale heterogeneity may be important for buffering mites from global warming. The results indicated that juvenile mites may be more vulnerable to global warming than adult stages. Importantly, the results also indicated that global warming may cause carbon and nitrogen losses in alpine and tundra mineral soils and that its effects may differ at local scale.Other Information Published in: Scientific Reports License: https://creativecommons.org/licenses/by/4.0See article on publisher's website: http://dx.doi.org/10.1038/srep44489

Global change is causing changes in temperature, precipitation, and nutrient availability. Alpine and polar regions are predicted to be among the most vulnerable for these changes. We applied a seven-year factorial experiment with warming and nutrient addition in two alpine vegetation communities. We analyzed relationship between fruit production and monthly mean, max and min temperatures during the fall of the pre-fruiting year, fruiting summer, whole fruit production period, and effects of summer and winter precipitation on fruit production. Nutrient addition and combined nutrient addition and warming increased total fruit production, and fruit production of graminoids in the later years in the Heath and Meadow and had a positive effect on forbs in the Meadow. In contrast fruit production of evergreen shrubs were negative affected by all treatments in the Meadow and Heath, while fruit production of deciduous shrubs was negatively affected in the Meadow. Minimum and mean temperatures were more important than max temperatures, and max temperatures of the fall before flowering was more important than max temperature during the flowering year. Winter precipitation had significant effect on total fruit production, fruit production of deciduous shrubs and forbs in the Heath, and on evergreen shrubs and forbs in the Meadow. Increased nutrient availability increased fruit production over time in contrasting high alpine plant communities, while experimental warming had no, or negative effect. Additionally, the results indicate that warmer summers may have limited impact on fruit production of high alpine plants. Instead, max temperatures during the fall before the fruiting year, and minimum temperatures may be more important. This study was supported by Carl Tryggers stiftelse för vetenskaplig forskning and Qatar Petroleum to JMA.

Litter decomposition is a key driver of ecosystem processes and carbon cycling. Decomposition rate is influenced by numerous factors, such as temperature, humidity, litter properties, soil properties, and properties of soil fauna/microbial communities. The aim of this review was to summarize current knowledge on litter decomposition above the treeline in alpine regions worldwide and identify: I) factors that have been studied in great detail, II) factors that have been less intensively investigated, III) geographical regions that have been less well studied, and IV) factors with consistent or inconsistent effects on decomposition. The review showed inconsistent results for all factors covered by two or more studies regarding their effect on decomposition rate (positive, negative, no effect), usually a result of interactions between factors. Studies examining one or several factors in the physical environment (i.e., altitude, experimental warming, microclimate, snow cover and soil moisture) were most common, while studies on different aspects of resource quality were the second most common. The impacts of trophic interactions on soil microbes and fauna were less frequently studied. Europe and Asia were the best-represented regions, in terms of number of studies and geographical distribution, while there were no studies from Africa and very few from South America and Australia. North American studies were all from Colorado, and those from Asia were all from China. In order to obtain better global representation, there is a need for studies in Africa, South America, and Australia. There is also a need for more studies to explain the large variation in responses of litter decomposition rates to different influencing factors in alpine environments. Future research should focus on interactions between different factors and on experiments testing specific relationships, such as the potential interaction between temperature and soil moisture and its effect on litter decomposition above the treeline in alpine regions. This study was supported by a grant from Qatar Petroleum ( QUEX-CAS-QP-RD-18/19 ).