The effect of severe drought on CO2 uptake by plants and carbon dynamics in the plant-soil system

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Drought events are regarded to increase in frequency and duration due to climate change. Especially, severe droughts most likely increase in Germany during summer season, where commonly plants actively grow and assimilate CO2, which can be strongly affected by drought. As the latter effect strongly depends on physiology of plants and drought resistance, more drought tolerant plants are thought to further assimilate CO2, while others die. This has a strong influence on the plant driven sequestration of C in soil and thus the C fluxes in the plant-soil system as drought might also promotes C loss in soil. Furthermore, it remains questionable, if plants are able to adapt to drought to further resist to severe droughts.In the current proposal, we will proof CO2 uptake by plants, translocation of C from plants to soil and soil C fluxes of two different plant communities (grass and heath), which were previously exposed to annual drought or control conditions, as affected by increasing drought. This will be traced in a triple 13CO2 pulse experiment, which was carried out under rainout shelters installed on the Bayreuth EVENT I experiment in summer 2011. After each 13CO2 labeling, carried out in weeks 1, 5, 9 after the installation of the rainout shelters, plant and soil samples were collected weekly, thus enabling 13C tracing in the individual plant compartments and soil, which is compared to replicates that did not receive the isotopic label.This research will serve the following central goals: 1. Determine effect of increasing drought on C uptake by plants and C translocation towards soil. 2. Identify plant species of lower or higher drought tolerance in both plant communities. 3. Assess the effect of severe drought on soil C storage. Such information is strongly required to understand plant community responses and carbon budgets in the plant-soil system as under future climatic conditions.