| Summary: | Alpine ecosystems have undergone significant modifications in recent years due to climate change. A trend towards reduced summer rainfall has been detected in various mountain regions, with warm, dry conditions predicted to intensify in some areas of the Alps by the end of the century. Together with increased frequency and magnitude of extreme events, new questions arise as to how climate change will impact ecosystem stability and functions. Although a number of studies have addressed the effects of warming on alpine ecosystems, responses to drier conditions remain poorly investigated. The main objective of the present research was to assess the effects of summer warming and reduced precipitation on key ecosystem functions of an alpine Carex curvula grassland over a 3-year period, with both field and lab experiments. The first field experiment investigated biomass production (Study 1) and litter decomposition (Study 2) in response to summer warming and chronic press drought. Increased temperatures were simulated using open top chambers, with rain-out shelters simulating historically-based, site-specific drought. Study 1 focused on the extent to which above- and belowground net primary production (ANPP and BNPP) were affected by treatments over 2 years; inter-annual ANPP differences, including the pre-treatment year, were also analysed. Results reveal that treatments do not influence ANPP, although there is wide inter-annual variation, whereas BNPP is lower under shelters. ANPP reveals a certain degree of resistance to short-term warming and extreme drought, but the difference between ANPP and BNPP underlines the need to take both compartments into account when assessing climate change effects on plant production. In Study 2, litter decomposition responses to treatments were analysed during one year (fall 2018-2019), with the influence of seasonality on litter quantity and quality also investigated to estimate the contribution of the long snow-covered season on the stability of decomposition processes under ...
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