Refractory and labile substances play a significant role in the dynamics
of soil organic matter and have key ecological functions. Only little
information, however, is available on the interactions between labile
substrates and biochar – a lack which hampers any prognoses of soil
processes and critical appraisals of biochar applications for improving
soil quality. This proposal aims at identifying transformation pathways
for substrates of increasing complexity in the order low molecular
weight organic substances, mucilage, fine roots and coarse roots in
contact with biochar in incubations. A mechanistic understanding of the
resulting biological, biophysical and biochemical interactions and
reactions will be achieved by employing dual isotopic labelling for
biochar (C-13) and substrates (C-14) and following the pathways using
biological analyses and soil partitioning into density and aggregate
fractions. The factorial experimental designs in combination with soil
biological, biophysical and biochemical analyses will allow elucidation
of the effects of substrates, substrate application rate, biochar age
and soil moisture on the interactions and pathways.Near and mid-infrared
spectroscopy in different measurement modes will be employed to
characterize the substrates, i.e. pure (freshly produced) biochar, light
fractions of the mixtures of soils and biochar during biochar ageing
and mixtures of soils, mucilage and fresh or aged biochar using band
assignments. Additionally, improved quantitative determinations using
the full spectra with foci on estimation accuracies for pure, coated and
aged substances will be achieved using an optimization of chemometric
approaches.The results of the dual isotopic labelling approaches in
combination with the spectroscopic approaches will give a mechanistic
understanding of the key processes explaining C stabilization by
biochars. Providing the tools to differentiate the impact of pure and
aged biochars on soil processes, this project will allow an improved
quantification and evaluation of the use of biochars in agriculture.