Molecular structures as drivers and tracers of terrestrial C fluxes - An ESF Network

 

Theme 1: Molecular composition and turnover of soil organic matter

Molecularly-uncharacterized organic matter comprises most organic carbon in soils and other terrestrial systems. Contrasting molecular structures display contrasting properties, which ultimately govern their fate in natural environments, but also control major soil functions.

SOM molecular properties with relation to soil functions are not only the concentration of organic matter, but also its hydrophobic or hydrophilic character that controls the soil water holding capacity. The affinity of SOM to the soil mineral matrix is decisive for the formation of soil structure. The origins, reactions and fates of these ubiquitous organic materials are relatively obscure, in large part because the rich vein of chemical information that typically derives from detailed structural and stereochemical analysis is yet to be tapped. But molecular investigations have recently played a key role in the understanding of SOM by providing molecular-level details about its composition.

New advanced techniques in organic and isotopic chemistry, both spectrometric and spectroscopic, are now giving us the capacity to probe for specific molecular structures of specific origin in soils and other natural environments. For example, 13C nuclear magnetic resonance (NMR) spectroscopy provides unsurpassed detail on the distribution of molecular functional groups within soils. Pyrolysis (Py) coupled to mass spectrometry (MS) and isotopic mass spectrometry (IRMS) allow us to analyze the distribution and turnover time of molecular structures and moieties within soil samples. Thermogravimetry and differential scanning calorimetry (TG/DSC) coupled to IRMS allow us to explore the turnover time of SOM across operationally-defined fractions.