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@PHDTHESIS{Wang:889995,
      author       = {Wang, Yi},
      title        = {{M}agnesiumstabile {I}sotope als {P}roxy für
                      biogeochemische {P}rozesse in terrestrischer
                      {U}mgebung{M}agnesium stable isotopes as a proxy for
                      biogeochemical processes in terrestrial environment},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      address      = {Aachen},
      publisher    = {RWTH Aachen University},
      reportid     = {FZJ-2021-00589},
      pages        = {115 pages},
      year         = {2019},
      note         = {Dissertation, RWTH Aachen, 2019},
      abstract     = {Magnesium (Mg) is the fourth most abundant element in the
                      Earth and plays a significant role in biological activities.
                      Processes involved in Mg cycle can fractionate Mg stable
                      isotopes, which makes Mg isotope systematics as a novel and
                      promising proxy in biogeochemistry. To improve our
                      understanding of Mg isotope fractionations in different
                      ecosystems, studies performed in this doctoral work include:
                      i) Mg isotope fractionation of plants under Mg deficient
                      environment, ii) Mg isotope fractionation in agricultural
                      system impacted by long-term anthropogenic soil practices,
                      and iii) Soil Mg isotope signatures in the Atacama Desert as
                      extreme environment of hyper-aridity. Magnesium deficiency
                      is detrimental to plant growth. However, an integrative
                      tracer revealing plant responses to Mg deficiency is still
                      lack. Here, Mg isotopes were used as an indicator with the
                      hypothesis that Mg deficiency could promote increased Mg
                      isotope fractionation in plants during uptake and subsequent
                      translocation processes. To test this hypothesis, wheat
                      plants (Triticum aestivum) were grown in a greenhouse under
                      Mg-sufficient and deficient conditions, and Mg
                      concentrations as well as their δ26Mg isotope compositions
                      in roots, stems, leaves and spikes at different growth
                      stages were analyzed. The results confirmed previous studies
                      that plants were systematically enriched in heavy isotopes
                      relative to the nutrient solution. This enrichment, however,
                      was more pronounced under low-Mg supply, which was
                      attributed to the increased contribution from active
                      transport system for Mg. With crop growth, the δ26Mg of
                      shoots shifted towards higher values under control but not
                      under low-Mg supply, reflecting a reduced root-shoot upward
                      translocation under low-Mg supply. At reproduction state,
                      light Mg was redistributed into the stems. Overall, initial
                      Mg supply can impact Mg isotope fractionation in plants and
                      assessing the Mg isotope compositions of plant organs
                      provides a useful indicator for different plant responses to
                      Mg supply from external environment. Liming is widely used
                      to alleviate soil acidity in western and central Europe.
                      However, its role on the cycling of Mg in arable soil-plant
                      systems is still not fully clarified. In the second part of
                      work, Mg concentrations and natural isotope compositions
                      with soil profiles and its vegetation (winter rye) from a
                      long-term agricultural experimental field with and without
                      liming practice were systematically analyzed. The results
                      showed that the δ26Mg signatures of the bulk Mg pool in
                      soil in the studied Albic Luvisol displayed limited
                      variation with depth and between trials. In contrast, the
                      exchangeable Mg pool in soil exhibited an apparent increase
                      of δ26Mg values along profile down to 50 cm depth,
                      especially in limed field with more negative shift of δ26Mg
                      than non-limed field. The observed enrichment of light Mg
                      isotopes in upper layers mainly resulted from the lime
                      deposition and plant uptake. An isotope-mixing model was
                      used to assess the respective contribution from lime
                      application and plant uptake to the Mg isotope compositions
                      in the exchangeable Mg pool in soil. The results indicated
                      that decades of liming practice presumably enhanced Mg
                      uptake by vegetation when comparing limed and non-limed
                      fields. However, no evidenced effects of liming on the
                      isotope compositions of plant Mg were observed. Winter ryes
                      grown on both limed and non-limed fields displayed identical
                      Mg isotope compositions with roots and spikes enriched
                      isotopically heavy Mg most. Silicate weathering is confirmed
                      to fractionate Mg isotopes in nature. However, how Mg
                      isotopes are fractionated under extreme climate is still not
                      reported. In the third part of this work, Mg isotope
                      compositions of surface soil layer with altitudinal gradient
                      (from 1300 to 2700 m a.s.l.) in the Aroma transect of the
                      Atacama Desert were analyzed. The surface soil Mg in the
                      Aroma transects is considered to stem from the mixing
                      deposition of both oceanic aerosols and the Andeans inputs.
                      With elevation decreased, soils Mg became isotopically
                      lighter. Enrichment of 26Mg at the site 2000 and 1300m a.s.l
                      indicated another Mg input or loss process. The δ26Mg
                      values in the pit soils from both the Aroma transect and
                      well-known Yungay site were positively related to the
                      weathering degree. Climatic aridity is assumed to change the
                      Mg isotope signatures by influencing weathering degree. The
                      present study for the first time reported soil Mg isotope
                      composition in such hyper-arid environment and suggested a
                      potential use of Mg isotopes to reconstruct the
                      paleoclimatic changes. To conclude, studies in this doctoral
                      work provided novel and comprehensive insights into Mg
                      isotope signatures and fractionations in biogeochemistry,
                      and improved the knowledge of Mg stable isotopes as a proxy
                      for biogeochemical processes in terrestrial environment.},
      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)11},
      doi          = {10.18154/RWTH-2019-11825},
      url          = {https://juser.fz-juelich.de/record/889995},
}