MOLTER Research theme 2

Research theme 2 supports activities aimed at deriving a comprehensive picture of molecular C fluxes in the plant-soil continuum, which includes frontier methods in organic chemistry as well as modelling and database development.

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

Plant molecular structures from above-ground residues and root activities represent the largest flux of C to the soil system. Only a small fraction of this large C input is eventually stabilised in soils. Understanding the molecular origin of this stabilised C is crucial to help maximize energy output from plant residues while increasing C storage in soils.

For a long-time, the lack of appropriate in situ methods meant that the fate of C derived from specific molecular structures was probed through laboratory incubations. These studies have heavily emphasized short-term mineralization rather than long-term C stabilization, while the latter is the relevant information in terms of C storage. This over-emphasis on short term mineralization has led us to misinterpretations. For example, lignin has long been considered as a major contributor to stable soil organic C because of its short term chemical recalcitrance to mineralization, while recent studies suggest that its long-term stabilization is not especially high. These recent studies are based on combined chemical (MS) and isotopic (IRMS) determination of molecular structures, which are isolated from soils either by wet chemistry or Py. Models of the molecular-C flux at the field scale are being adapted to these emerging datasets.

As a result, a new paradigm for the stabilisation in soils of plant C derived from specific molecular structures is currently emerging. Recent investigations have addressed, among others, macromolecules such as lignin, polysaccharides, tannins, cutins and suberins, and simpler molecules such as sugars and amino acids.