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@PHDTHESIS{Xing:886095,
      author       = {Xing, Ying},
      title        = {{I}ron isotope fractionation in arable soil and
                      graminaceous crops},
      volume       = {517},
      school       = {Universität Bonn},
      type         = {Dissertation},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2020-04263},
      isbn         = {978-3-95806-509-3},
      series       = {Schriften des Forschungszentrums Jülich. Reihe Energie
                      $\&$ Umwelt / Energy $\&$ Environment},
      pages        = {123 S.},
      year         = {2020},
      note         = {Universität Bonn, Diss., 2020},
      abstract     = {Soils contain large quantities of Fe, however, the
                      Fe-solubility is very low. Plants have developed two
                      efficient strategies to secure Fe uptake from soil under
                      Fe-deficient conditions: (i) the sequential
                      acidification-reduction-transport strategy (strategy I) and
                      (ii) the chelation-based strategy (strategy II). All
                      processes involved in the Fe cycle in soil-plant systems can
                      fractionate stable Fe isotopes. Hence, I (i) conducted a
                      systematic review about the state of Fe isotope researchin
                      plant studies and highlighted the research gaps. Then I
                      supplemented this theoretical study by two experiments: I
                      (ii) examined the effect of different Fe availabilities on
                      Fe isotope fractionation in wheat plants under controlled
                      conditions and I (ii) investigated the effect of 50 years of
                      irrigation on Fe isotope fractionation in soils and cereals
                      in a long-term field experiment. My review suggested that
                      strategy I plants especially take up light Fe isotopes,
                      while strategy II plants fractionate less towards light
                      isotopes. Above ground tissues usually show even lighter Fe
                      isotope signatures than the roots, with flowers
                      (δ$^{56}$Fe: -2.15 to -0.23‰) being isotopically the
                      lightest. I found that all reported strategy I plants
                      consistently enriched light Fe isotopes under all growth
                      conditions. Strategy II plants, however, could be enriched
                      with either light or heavy Fe isotopes, depending on the
                      growth conditions. Depending on the Fe speciation and
                      concentration present in the growth medium, some strategy II
                      plants like rice are able to adapt their uptake strategy as
                      they also possess ferrous transporters and are hence also
                      able to take up Fe(II) ions. In a greenhouse study, I
                      cultivated summer wheat ($\textit{Triticum aestivum L.}$)
                      under Fe-sufficient(control, 0.0896 mM Fe-EDTA) and
                      deficient (Fe-deficient, 0.0022 mM Fe-EDTA) conditions.
                      Plants were sampled at different growth stages (vegetative
                      and reproductive growth stages) and separated into different
                      plant organs (root, stem, leaf, spike/grain). All samples
                      were analyzed for their Fe concentrations and δ$^{56}$Fe
                      isotope compositions. The results showed that Fe-deficiency
                      reduced the whole plant Fe mass by 59\% at vegetative
                      growth. During reproductive growth, Femass fluxes indicated
                      different preferential Fe translocation pathways under
                      different Fe supply. Under Fe-deficient conditions, Fe
                      uptake from growth substrate increased whereas under Fe
                      sufficient conditions Fe was preferentially redistributed
                      within the plant. Under Fe-sufficient conditions
                      increasingly lighter δ$^{56}$Fe values from older to
                      younger plant parts were found, but no indications that the
                      chelation-based uptake strategy was activated. However, with
                      serious shortage of Fe, the shift towards lighter
                      δ$^{56}$Fe values was reduced. This suggested that Fe
                      isotope ratios can reflect both wheat growth conditions and
                      ages. In a field study, I sampled wheat plants and Retisol
                      soil cores down to a depth of 100 cm from along-term
                      irrigation treatment at Berlin-Thyrow. The irrigated plots
                      had higher Fe avail concentrations than the non-irrigated
                      plots in the top 40 cm of soil, but there were no changes in
                      δ$^{56}$Fe values. Due to the research site being one of
                      the driest areas in Germany with hardly ameaningful water
                      percolation, the maximum difference of δ$^{56}$Fe$_{avail}$
                      values between 40 to 50 cm and 70 to 100 cm was explained
                      soil pedogenesis rather than irrigation treatment. The wheat
                      plants grown in both irrigated and non-irrigated plots were
                      slightly enriched in light Fe isotopes, exhibiting similar
                      δ$^{56}$Fe values to those of the respective topsoil. I
                      concluded that the overall δ $^{56}$Fesignature of wheat
                      was regulated by plant-homeostasis and specific on-site soil
                      characteristics, whereas irrigation had little if any
                      significant effect on the Fe isotopes in the crops. Overall,
                      my study showed that the Fe isotope compositions of wheat
                      plants were not affected by Fe availabilities in substrate
                      until the anthesis stage. However, during the reproductive
                      growth phase with sufficient Fe supply, δ$^{56}$Fe values
                      of different plant organs showed significant Fe
                      fractionation. The former processes were hardly affected by
                      irrigation.},
      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)3 / PUB:(DE-HGF)11},
      urn          = {urn:nbn:de:0001-2020120304},
      url          = {https://juser.fz-juelich.de/record/886095},
}