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@ARTICLE{Gangi:173296,
      author       = {Gangi, Laura and Tappe, Wolfgang and Vereecken, Harry and
                      Brüggemann, Nicolas},
      title        = {{E}ffect of short-term variations of environmental
                      conditions on atmospheric {CO}18{O} isoforcing of different
                      plant species},
      journal      = {Agricultural and forest meteorology},
      volume       = {201},
      issn         = {0168-1923},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2014-06707},
      pages        = {128 - 140},
      year         = {2015},
      abstract     = {The oxygen isotope signature of atmospheric carbon dioxide
                      (δ18O–CO2) is significantly influenced by terrestrial
                      vegetation through 18O-exchange between CO2 and leaf water.
                      However, the impact of short-term variations of
                      environmental conditions on this 18O-exchange has not been
                      sufficiently characterized yet for different plant
                      functional types. In the present study, δ18O of CO2 and
                      water vapor were measured online in chamber-based
                      experiments with spruce, wheat, poplar and maize using
                      infrared laser spectroscopy. The impact of the plants on
                      ambient δ18O–CO2 was inferred from the chamber-based
                      CO18O isoforcing (CO18O-Iso), i.e., the product of the net
                      CO2 flux through the chamber and the δ18O–CO2 of this
                      flux obtained from differential measurements at the chamber
                      inlet and outlet. The measured CO18O-Iso was compared to the
                      CO18O isoforcing (CO18O-Isosim) calculated as a function of
                      the δ18O of leaf water at the evaporation site
                      (δ18O–H2Oev) and the degree of oxygen isotope
                      equilibration between CO2 and leaf water (θ). Plants were
                      exposed to elevated air temperature (35 °C) and cessation
                      of water supply. CO18O-Iso was reduced at 35 °C due to the
                      reduction of stomatal conductance (gs) in all plant species
                      except for maize, and at decreasing water availability in
                      all four plant species due to a reduction of θ,
                      assimilation rate (Ar) and gs, while leaf water became
                      progressively 18O-enriched. The combination of θ, gs, Ar
                      and δ18O–H2Oev accounted for up to $98\%$ of the
                      variations in CO18O-Iso, which were well represented by
                      CO18O-Isosim, whereas the relationship between individual
                      determinants and CO18O-Iso was weaker. The degree of
                      isotopic CO2–H2O equilibration calculated from isotopic
                      gas exchange reached maximum values of 0.51 and 0.53 in
                      maize and spruce, and 0.67 and 0.74 in wheat and poplar,
                      respectively. Although θ was highly sensitive to the
                      parameterization of mesophyll conductance (gm), most of the
                      gm literature values for each species yielded values for θ
                      significantly lower than previously reported for the
                      respective plant species. This finding, as well as the
                      observed temporal variations in the oxygen isotopic exchange
                      introduced by varying environmental conditions, should be
                      considered for the parameterization of δ18O–CO2 models.},
      cin          = {IBG-3},
      ddc          = {630},
      cid          = {I:(DE-Juel1)IBG-3-20101118},
      pnm          = {255 - Terrestrial Systems: From Observation to Prediction
                      (POF3-255) / 255 - Terrestrial Systems: From Observation to
                      Prediction (POF3-255)},
      pid          = {G:(DE-HGF)POF3-255 / G:(DE-HGF)POF3-255},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000347863900013},
      doi          = {10.1016/j.agrformet.2014.10.015},
      url          = {https://juser.fz-juelich.de/record/173296},
}