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@INPROCEEDINGS{vanDusschoten:1020588,
      author       = {van Dusschoten, Dagmar and Pflugfelder, Daniel and Kochs,
                      Johannes},
      title        = {{R}oot water uptake in relation to plant transpiration},
      reportid     = {FZJ-2024-00283},
      year         = {2023},
      abstract     = {Typically, root water uptake (RWU or Utot) is said to be
                      driven by transpiration (Tr). It is however more accurate to
                      state that transpiration causes a reduction in leaf water
                      content that reduces the leaf water potential such that a
                      water potential gradient builds up between leafs and soil
                      water, such that water can be extracted from the soil. For
                      herbaceous plants, the amount of water that is hereby lost
                      is typically assumed to be negligible so the plant can be
                      treated as a resistive system. In how far this is true is
                      open to discussion as quantifying shoot water changes is not
                      easily feasible, especially when the soil-root system is
                      drying out. A balance cannot observe water moving between
                      the soil and the shoot and shoots have empty spaces such
                      that 3D cameras provide an incomplete picture. Shoot weight
                      determination requires that the amount of soil water is
                      independently assessed to discriminate between the two pools
                      of water. This can be achieved when a balance is combined
                      with a Soil Water Profiler (SWaP) on the same soil-plant
                      system. The precision of the SWaP is comparable to that of
                      an expensive balance (<10mg for a 6kg system). Here we
                      performed experiments with the SWaP – balance combination
                      under modulated light with progressive soil dehydration for
                      sunflower and faba beans (N=4). Our data shows that
                      transpiration precedes Utot by about 5 to 10 mins under wet
                      conditions (pF<2.5) and Utot can exceed Tr by up to $20\%.$
                      Gradually, with decreasing soil water content we find that
                      Utot becomes smaller than Tr and at the same time the delay
                      between Tr and Utot increases. For pF>3 most of the
                      transpired water stems from the shoot, not from root water
                      uptake, indicating that Tr is a poor proxy for RWU for pot
                      experiments where soil is drying at a rate of $~5\%$ per day
                      at well watered conditions. This is very important for
                      calculations of root conductance during drying scenarios. We
                      found significant differences between sunflower sensitivity
                      to soil drying as compared to faba beans that are somewhat
                      more sensitive. We also present data that shows that the
                      delay between Tr and local water uptake is rather dependent
                      on depth and not so much dependent on local pF, which is
                      typically lower for shallow sections of the pot. This may
                      potentially be explained by loss of root water when Tr
                      increases with light, analogous to shoot water losses, as
                      the soil dries.},
      month         = {Apr},
      date          = {2023-04-24},
      organization  = {EGU General Assembly 2023, Vienna
                       (Austria), 24 Apr 2023 - 29 Apr 2023},
      subtyp        = {After Call},
      cin          = {IBG-2},
      cid          = {I:(DE-Juel1)IBG-2-20101118},
      pnm          = {2171 - Biological and environmental resources for
                      sustainable use (POF4-217)},
      pid          = {G:(DE-HGF)POF4-2171},
      typ          = {PUB:(DE-HGF)6},
      doi          = {10.5194/egusphere-egu23-12018},
      url          = {https://juser.fz-juelich.de/record/1020588},
}