Biogenic carbonate in soils

This aspect of our research concerns the processes leading to the accumulation of secondary calcium carbonate (CaCO₃) in the soils and its relationship with the associated vegetation and microorganisms. The approach centers more specifically on two different habits of calcite : needle fibre calcite (or NFC) and nanofibers (Figure 1 and 2). The origin of these two forms particular to calcite is the subject of a controversy over its physico-chemical vs. biological origin.
The current research involving biogeochemical, isotopic, petrographic studies, and laboratory experiments shows that these crystals are definitely of fungal origin. This project highlights the potential role of fungi in carbon sequestration in continental environments. Because fungi are found everywhere in terrestrial environments, this study concentrates on understanding their fundamental role, as well as that of organic material, in the coupled cycle of carbonate-carbon in terrestrial environments.

Figure 1 : Sketch illustrating the possible hypotheses for the formation of needle fiber calcite (left) and calcite nanofibers (right).

Figure 2 : SEM images of various needle fiber calcite (NFC) morphologies. (A) Simple NFC, (B) rhomboedral calcite overgrowth onto single NFC, (C) nanofiber mesh associated with NFC, (D) NFC forming a bundle.

For more information:

Bindschedler S., Millière L., Cailleau G., Job D. & Verrecchia E.P. (in press): An ultrastructural approach to analogies between fungal structures and needle fibre calcite. Geomicrobiology Journal.

Millière L., Hasinger O., Bindschedler S., Cailleau G., Spangenberg J. E. & Verrecchia E.P. (2010): Stable carbon and oxygen isotope signature of pedogenic needle fibre calcite. Geoderma.

Bindschedler S., Millière L., Cailleau G., Job D. & Verrecchia E.P. (2010): Calcitic nanofibers in soils and caves: a putative fungal contribution to carbonatogenesis. Geological Society of London Special Publications 336, 225-238.

Cailleau G., Dadras M., Abolhassani-Dadras S., Braissant O. & Verrecchia E.P. (2009): Evidence for an organic origin of pedogenic calcitic nanofibres. Journal of Crystal Growth 311, 2490-2495.

Cailleau G., Verrecchia E.P., Braissant O. & Emmanuel L. (2009): The biogenic origin of needle fibre calcite. Sedimentology 56, 1858-1875.

Braissant O., Cailleau G., Dupraz C. & Verrecchia E.P. (2003): Bacterially induced mineralization of calcium carbonate in terrestrial environments : The role of exopolysaccharides and amino acids. Journal of Sedimentary Research 73, 485-490.

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