Tropical soils and the oxalate-carbonate pathway

In the intertropical zone, the oxalate-carbonate pathway observed underneath certain tropical trees like iroko (Figure 1) is surprisingly very well developed. Through photosynthesis, the trees accumulate large quantities of calcium oxalate, a very insoluable organic acid, forming crystals in their tissues. But these oxalate crystals do not accumulate in the soil after the decomposition of the plant tissues by the fungi and other heterotrophic organisms. They are consumed by bacteria present in the soil that convert them into calcium carbonate. This phenomenon is a net carbon trap in which the initial CO₂ is atmospheric. The Biogeosciences Laboratory works on several tropical forests in tropical Africa, India, and Amazon. This phenomena is widely documented in the intertropical zone, where it could lead to important applications related to reforestation, sustainable management of forests, and agro-sylviculture, and at the same time, make a significant contribution to the carbon dioxide trapping.
 

Figure 1 : (left) Iroko tree, Cameroon. (right) SEM image of oxalate crystals in iroko wood.

For more information:

Cailleau G., Braissant O., Dupraz C., Aragno M. & Verrecchia E.P. (2005): Biologically induced accumulations of CaCO₃ in orthox soils of Biga, Ivory Coast. Catena 59, 1-17.

Braissant O., Cailleau G., Aragno M. & Verrecchia E.P. (2004): Biologically induced mineralization in the tree Milicia excelsa (Moraceae) : its causes and consequences to the environnement. Geobiology 2, 59-66.

Cailleau G., Braissant O. & Verrecchia E.P. (2004): Biomineralization in plants as a long-term carbon sink. Naturwissenschaften 91, 191-194.

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