Research theme 5 supports activities aiming at identifying, quantifying and fate-tracing of dissolved organic molecular structures in terrestrial environments.

Theme 5: Dissolved organic molecules in soils: origin, functionality and transport

Dissolved organic molecules present in soil solution represent a wide variety of compounds from high to low molecular mass being both hydrophilic and hydrophobic, some of which probably bear significant ecosystem functions, such as complex-forming ligands and siderophores.

High molecular mass molecules, operationally defined as humic acids, have been suggested to be supramolecular associations. The sources of dissolved organic molecules are mainly litterfall, root litter, root exudates and microbial production. The sinks are adsorption and precipitation in the soil, mineralization to CO2 and leaching out of the soil. Investigating molecular structures helps us evaluate interactions in the plant-mycorrhiza-bacteria-soil system, and their impact on the ecosystem C balance.

By using molecular techniques such as Liquid Chromatography coupled to Tandem Mass Spectrometry (LC-MS/MS) or Inductively Coupled Plasma Mass Spectrometry (LC-ICP-MS) for studying complexation with metals, molecules of significance can be determined. Also near-edge structure spectroscopy (XANES) is used to study complexation with sulphur containing molecules, and NMR techniques are used for identification of functional groups. By these and other techniques, the fate of dissolved organic molecules in the plant-soil-water continuum can be followed, which helps us understand its significance for terrestrial ecosystem functioning.  

Theme 1: Molecular composition and turnover of soil organic matter

Theme 2: Plant molecular structures as drivers of C stabilisation in soils

Theme 3: Fire transformations of plant and soil molecular structures

Theme 4: Molecular markers in soils