The soil structural stability of termite nests: role of clays in Macrotermes bellicosus (Isoptera, Macrotermitinae) mound soils

Fungus-growing termites enrich their nest structures with clays and can modify the mineralogical properties of silicate clays. In order to determine the role of clay in soil structural stability of mounds, we measured the physico-chemical properties and the water behaviour of termite mound soil. Two opposing tendencies control the structural stability of termite mound soil: (i) the increase of clay content in the mound leading to a decrease of pore sizes and rate of water diffusion; and (ii) the swelling of 2:1 clay types when water penetrates into the soil leading to a breakdown of the mound soil. Although soil organic matter (SOM) is usually considered as a cement ensuring the soil structural stability of mound soil, this study shows that SOM has a negligible role and that clay can be considered as a key component to understand the structural stability of Macrotermes mound soil.