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@ARTICLE{VelascoMolina:255947,
      author       = {Velasco-Molina, Marta and Berns, Anne E. and Macías,
                      Felipe and Knicker, Heike},
      title        = {{B}iochemically altered charcoal residues as an important
                      source of soil organic matter in subsoils of fire-affected
                      subtropical regions},
      journal      = {Geoderma},
      volume       = {262},
      issn         = {0016-7061},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier Science},
      reportid     = {FZJ-2015-06026},
      pages        = {62 - 70},
      year         = {2016},
      abstract     = {Although climatic conditions of subtropical regions support
                      fast biochemical degradation of soil organic matter (SOM),
                      some of their soils reveal dark umbric horizons with
                      considerably high organic C contents. Since such soils can
                      reach a depth of several meters a better understanding of
                      the processes involved in the humification of its SOM is
                      essential for an improved elucidation of the impact of the
                      hot and humid conditions of subtropical regions on global C
                      cycling. Therefore, the SOM of three Umbric Ferralsols from
                      Brazil was characterized for its quantity and chemical
                      composition as a function of soil depth. Solid-state 13C
                      nuclear magnetic resonance (NMR) spectra revealed an
                      increase of the aromaticity with soil depth to exceptionally
                      high values between 40 and $70\%$ of the SOM. Chemical
                      oxidation of the SOM with acid potassium dichromate
                      confirmed that a major part of this C group is attributable
                      to pyrogenic organic matter (PyOM). High carboxyl-C contents
                      between 13 and $21\%$ of the total organic C in the subsoils
                      showed that their PyOM is strongly oxidized, most likely due
                      to previous intense biochemical reworking. Since the latter
                      improves the water solubility of the formerly hydrophobic
                      charcoal residues, such oxidized PyOM can be transported
                      with the soil solution into deeper soil horizons. As
                      indicated by the pattern of the 13C NMR spectra and the high
                      C contents of the subsoil, the partially degraded PyOM seems
                      to have lost its attractiveness to microbial attack with
                      ongoing downward movement and accumulation. Correlating
                      parameters of organic matter with those of soil mineralogy
                      suggested that in addition to stabilization by the mineral
                      phase other mechanisms must have contributed to the
                      persistence of PyOM in the studied soils. Considering that
                      in soils, microbial degradation of aromatic structures is
                      mainly performed by lignolytic and aerobic organisms, we
                      suggest that increasing oxygen depletion and unfavorable
                      living conditions in the deeper soil regions decreased the
                      activity of those organisms. This enhanced the biochemical
                      recalcitrance of the aromatic PyOM whereas non-pyrogenic SOM
                      was still subjected to degradation although most likely at a
                      slower rate. As a consequence, the selective preservation of
                      PyOM shifted not only the quality of the subsoil SOM toward
                      higher aromaticity but also increased its quantity. Based on
                      our results, we concluded that downward translocation of
                      partially degraded PyOM and its subsequent accumulation
                      represent important processes in soil systems which are
                      frequently affected by fires.},
      cin          = {IBG-3},
      ddc          = {550},
      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:000362308300007},
      doi          = {10.1016/j.geoderma.2015.08.016},
      url          = {https://juser.fz-juelich.de/record/255947},
}