Kurzbeschreibung
(Englisch)
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In the proposed project, we will synthesize data from a long-term global change experiment to study how ecosystem functions at alpine treeline might change under future atmospheric and climate conditions. The Stillberg treeline experiment (Davos, Switzerland) included 9 years of CO2 enrichment (+200 ppm; 2001-2009) and 6 years of soil warming (+4°C; 2007-2012). The study contained two key treeline species, Larix decidua and Pinus uncinata, growing in dwarf shrub heath vegetation. In 2012, a complete harvest was conducted of all trees (including entire root systems), above-ground understorey vegetation, fine roots and soil. Here, we propose to conduct detailed measurements of this material and to synthesize harvest data with data collected during the 12-year experiment. An in-depth analysis and synthesis of these data will provide novel information about tree biomass and allocation, root growth, and ecosystem carbon and nutrient pools. Moreover, the relatively long experimental duration allows us to capture potential responses and feedback processes that only occurred after several years. Specifically, we will address 1) How did elevated CO2 and soil warming, separately and combined, affect the structure and biomass allocation of the two tree species? 2) How did the experimental climate change influence ecosystem carbon fluxes and pool sizes in this treeline ecosystem? 3) Did the treatments alter nitrogen dynamics through the plant and soil system?
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Abstract
(Englisch)
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Cold temperature limited ecosystems such as treelines are likely to respond particularly sensitive to climatic changes. In the proposed project, we will synthesize data from a long-term global change experiments to study how ecosystem functions at alpine treeline might change under future atmospheric and climate conditions. The Stillberg treeline experiment (Davos, Switzerland) included 9 years of CO2 enrichment (+200 ppm; 2001-2009) and 6 years of soil warming (+4°C; 2007-2012). The study contained two key treeline species, Larix decidua and Pinus uncinata, growing in dwarf shrub heath vegetation. In 2012, a complete harvest was conducted of all trees (including entire root systems), above-ground understorey vegetation, fine roots and soil, which we analysed in this project. In addition, we have analysed soil microbial community structure using 454-pyrosequencing. In addition, we assessed fine root biomass and extrametrical mycelia using a ‘space for time’ substitution approach along four elevational gradients reaching from the tundra to the forest ecotone in the Ural mountains with well-documented climate-change driven treeline advances. Results showed that plant responses to elevated CO2 and soil warming were highly species specific with Larix and Vaccinium myrtillus showing growth stimulation to elevated CO2, while no changes occurred in final total biomass production in the other species. In contrast, warming induced a considerable growth stimulation in Pinus (but not Larix) and also in Vaccinium, while herbaceous plant biomass declined. Our assessment of belowground communities showed that soil warming but not CO2 enrichment affect soil fungal communities. Soil warming led to a 5-fold increase in fruiting bodies of the dominant Lactarius rufus. Moreover, DNA analysis revealed that the fungal community shifted towards a greater abundance of nitrophilic species. These findings are supported by higher contents of available nitrogen in the soils resulting from an enhanced mineralization of soil organic matter. Along the altitudinal gradients representing indirect effects of climatic changes via vegetation shifts, here treeline advances, fine root biomass decreased by 40% from the tundra to the forest. Path analysis indicated that shifts in the tree and understory vegetation cover, associated with treeline advances, were a strong driver of changes in root biomass and soil carbon storage. Results also showed that the ratio between below- and aboveground biomass decreased from the treeline to the forest. Overall, our results show global change in high-altitude ecosystems (elevated CO2, warming) will induce species-specific growth responses above – and below the ground. In addition, our findings indicate a strong impacts on ecosystem’s carbon and nutrient cycle and other functions of alpine treeline ecosystems which may feedback on the ongoing climatic changes.
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