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Background:In those alpine regions where growing season precipitation is decreasing due to climate change, the capacity of soils to retain water may become an important factor for the persistence of plant species. However, the importance of soil water storage capacity (WSC) for plant species diversity has not been studied so far. Aims:We aim to evaluate the relevance of WSC for species diversity of alpine plant communities in relation to temperature and length of growing season. Methods:Species diversity was determined in 150 plots from a broad range of alpine vegetation types in the calcareous western part of the central Swiss Alps. WSC of soil cores sampled in every plot was determined, as well as rooting zone temperature and snowmelt date. Linear mixed models were used to assess the relationship between environmental data and species diversity. Results:Species diversity was most strongly and positively related to WSC, followed by mean daily minimum temperature (Tmin) of the growing season. Species diversity was significantly related to date of snowmelt only in sites with high WSC and/or Tmin. Conclusions:WSC represents an integrative measure for habitat quality and accounts for differences in species diversity within the study region. In order to understand and predict responses of plant species to climate change in high mountain regions, it may be crucial to also take changes in plant water supply into account. [ABSTRACT FROM PUBLISHER]