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@ARTICLE{Amelung:256540,
      author       = {Amelung, Wulf and Antar, P. and Kleeberg, I. and Oelmann,
                      Y. and Lücke, Andreas and Alt, F. and Lewandowski, Hans and
                      Pätzold, S. and Barej, J. A. M.},
      title        = {{T}he δ$_{18}${O} signatures of {HC}l-extractable soil
                      phosphates: methodological challenges and evidence of the
                      cycling of biological {P} in arable soil},
      journal      = {European journal of soil science},
      volume       = {66},
      number       = {6},
      issn         = {0022-4588},
      address      = {Oxford [u.a.]},
      publisher    = {Wiley-Blackwell},
      reportid     = {FZJ-2015-06424},
      pages        = {965-972},
      year         = {2015},
      abstract     = {Soil phosphates exchange oxygen atoms rapidly with soil
                      water once recycled by intracellular enzymes, thereby
                      approaching an equilibrium δ18OP signature that depends on
                      ambient temperature and the δ18OW signature of soil water.
                      We hypothesized that in the topsoil, phosphates reach this
                      equilibrium δ18OP signature even if amended by different
                      fertilizers. In the subsoil, however, there might be
                      phosphates with a smaller δ18OP value than that represented
                      by the isotopic equilibrium value, a condition that could
                      exist in the case of limited biological P cycling only. We
                      tested these hypotheses for the HCl-extractable P pool of
                      the Hedley fractionation scheme of arable soil in Germany,
                      which integrates over extended time-scales of the soil P
                      cycle. We sampled several types of fertilizer, the surface
                      soil that received these fertilizer types and composites
                      from a Haplic Luvisol depth profile under long-term
                      agricultural practice. Organic fertilizers had significantly
                      smaller δ18OP values than mineral fertilizers.
                      Intriguingly, the fields fertilized organically also tended
                      to have smaller δ18OP signatures than other types of
                      surface soil, which calls into question full isotopic
                      equilibrium at all sites. At depths below 50 cm, the soil
                      δ18OP values were even depleted relative to the values
                      calculated for isotopic equilibrium. This implies that
                      HCl-extractable phosphates in different soil horizons are of
                      different origins. In addition, it supports the assumption
                      that biological cycling of P by intracellular microbial
                      enzymes might have been relatively inefficient in the deeper
                      subsoil. At depths of 50–80 cm, there was a transition
                      zone of declining δ18OP values, which might be regarded as
                      the first evidence that the degree of biological P cycling
                      changed at this depth interval},
      cin          = {IBG-3},
      ddc          = {630},
      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)16},
      UT           = {WOS:000364312500001},
      doi          = {10.1111/ejss.12288},
      url          = {https://juser.fz-juelich.de/record/256540},
}