Mineral surfaces and organic matter accrual in soils

Soil is a dynamic and hierarchically organized system of organic and inorganic constituents, the spatial structure of which defines a large, complex and heterogeneous biogeochemical interface of pores and aggregates. The aggregates are resulting from soil forming processes involving association of organic and mineral materials at the molecular scale, and determine major soil functions. Our approach consists of controlled incubation experiments combined with investigations of natural soils taking advantage of natural gradients of soil texture or time of soil formation. The spatial distribution of elements characteristic of organic matter (OM) (C or N) and minerals (e.g., Fe, Al, O, or Si) in soils at the sub-micrometer scale allows to map different soil components and to elucidate their association within the soil microstructure. These studies reveal that OM occurs in patches, and the surface is only partly covered with OM. This sustains a coexistence of soil functions provided by mineral surfaces beyond OM sequestration. The decoupling of OM sequestration from the proportion of mineral surfaces in the soil implies that there is no limit predetermined by clay content for the capacity of soils to sequester organic carbon.

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Invited by Stefan Peiffer, Hydrology