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@MASTERSTHESIS{Khnhammer:857047,
      author       = {Kühnhammer, Kathrin and Merz, Steffen and Brüggemann,
                      Nicolas and Vereecken, Harry and Rothfuss, Youri},
      title        = {{M}onitoring root water uptake of {C}entaurea jacea using
                      water stable isotopes},
      school       = {Universität Freiburg},
      type         = {Masterarbeit},
      reportid     = {FZJ-2018-06315},
      pages        = {118},
      year         = {2018},
      note         = {Masterarbeit, Universität Freiburg, 2018},
      abstract     = {Root water uptake plays a crucial role in the water cycle,
                      as it is the largest flux on land surfaces returning water
                      to the atmosphere. Its complex dynamics and ecosystem
                      feedbacks are however still not well understood and can
                      therefore not be adequately accounted for in models
                      simulating water transport in the soil-plant-atmosphere
                      interface. Especially on short time scales, high uncertainty
                      exists with regards to the plasticity of water uptake and
                      its associated driving forces. In view of an increase in
                      hydrological extremes and a changing climate, a more
                      mechanistic understanding is however crucial.For five
                      decades, water stable isotopes substantially improved our
                      knowledge about this hard to observe belowground process.
                      However, monitoring short-term variations was restricted,
                      due to the necessity for destructive sampling and laborious
                      sample analysis. Recent methodological advances now offer
                      new possibilities to overcome these constraints and
                      triggered the development of new approaches, which enable an
                      in-situ monitoring of water stable isotopes in soil water
                      and water taken up by plants. First combined in-situ
                      measurements were already conducted in trees, but have not
                      yet been applied to the examination of root water uptake in
                      herbaceous species.In the presented work, a new method is
                      tested that allows for long-term in-situ sampling of water
                      stable isotopes across a soil column and in plant
                      transpiration under controlled conditions in the laboratory,
                      using Cavity Ring-Down Spectroscopy.For this purpose, an
                      existing soil column setup is further developed and expanded
                      by a plant component. Dual isotope data in daily and
                      sub-daily temporal resolution is collected across soil
                      isotopic profiles and transpiration of Centaurea jacea,
                      respectively. It will be shown that measured transpiration
                      values reflect a mixture of soil water differing in its
                      isotopic composition across the profile throughout a period
                      of six weeks, despite pronounced dynamic changes in both
                      systems. Derived measurement precision is comparable to that
                      of established and also other newly developed in-situ
                      methods. The setup proved to be an adequate tool for
                      capturing short-term variations in root water uptake in
                      response to differences of water availability in daily
                      resolution. To visualize water uptake profiles, data sets of
                      the isotopic composition in plant transpiration and soil
                      profiles are combined in a statistical multi-source mixing
                      model. Observed trends can logically be interpreted with
                      existing knowledge on water uptake dynamics and plasticity,
                      while highlighting knowledge gaps in the mechanistic
                      understanding of contributions of underlying processes.
                      Prospectively, the implementation of data sets, obtained
                      with the tested method, in mechanistic state-of-the-art
                      models could help to further disentangle complex
                      interactions between soils and root systems. On the other
                      hand modeling approaches across scales that now more
                      commonly include water stable isotopes, will potentially
                      benefit from recorded time series. Therefore temporally
                      highly resolved data sets should be collected for a rangeof
                      plant species, soil types and scenarios in the future.},
      cin          = {IBG-3},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)19},
      url          = {https://juser.fz-juelich.de/record/857047},
}