Scientific Project A3 - Initial stages of
humus development
Staff
The mechanisms of soil organic matter (SOM) transformation and stabilisation
operate on different time scales. We hypothesize that in the initial stage
of terrestrial humus formation the selective accumulation of recalcitrant
organic matter and the development of hydrophobic surfaces are the dominatin
mechanisms. These processes are highly affected by pioneer vegetation
development and succession. In the initial phase of ecosystem development,
the sources for SOM formation change over time. At long-term scales, stable
organo-mineral associations and microaggregation become important after
weathering and formation of secondary minerals. Both, the recalcitrance and
bioavailability of the accumulating SOM pool are influenced by the formation
of organic matter in different soil structures (biogenic crusts, coatings on
primary particles, aggregates, pores, rhizosphere).
The subproject A3 intends to identify and quantify relationships between
processes of humus formation (origin and quality of organic matter, binding
form) and the generation of soil structure (aggregation, hydrophobic
surfaces) during initial soil development. The study areas include
experimental and reference sites (glacier forefield, sand dunes) and
represent initial ecosystems with natural succession (mainly grasses) on
sandy substrates.
Parameters indicating the state of soil OM and soil profile development to
be determined are:
• degree of development and thickness of soil profiles
• characteristics of structures which store humus (biogenic crusts,
aggregates, organic surface layers) and accumulation of free and occluded
particulate organic matter
• surface characteristics of mineral particles (specific surface, organic
matter loading, wettability)
• chemical composition of organic materials
• amount and composition of organo-mineral associations
For this purpose the following combination of techniques will be applied:
• soil fractionation according to particle size and density to separate
plant residues (particulate organic matter) from organo-mineral associations
(heavy fractions)
• chemolytic techniques and CPMAS 13C NMR spectroscopy to determine the
composition and origin of organic compounds
• characterisation of heavy fractions and sorption experiments of dissolved
organic carbon (DOC) to investigate the formation of organo-mineral
associations
• FTIR microscopy and synchrotron tomography to scan the location of organic
matter stabilisation and to relate chemical and physical properties to
specific structures
• determination of degree and persistence of hydrophobicity (effective and
potential) to characterise the wettability as parameter for turnover and
stabilisation of soil organic matter
After identification of origin, chemistry and types of organic matter
accumulation in different stable fractions we deduce the essential processes
and structures of humus formation, stabilisation and their change during
initial soil development. The results will be used for the dynamic
structural and process model to be developed within the framework of SFB/TRR
38.
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