Variation in the distribution of monosaccharides in soil fractions in the mounds of termites with different feeding habits (Senegal)

Abstract.

The comparative impact of the two most representative species of termites (Cubitermes niokoloensis and Macrotermes bellicosus) on the monosaccharide (glucose, galactose, mannose, rhamnose, arabinose, and xylose) content of soil from a semi-arid tropical savanna (Senegal) was investigated. Two complementary procedures for soil fractionation (particle-size fractionation vs. aggregate-size fractionation) were carried out on a control soil (not subjected to the influence of termites) and on the soil of the internal wall (IW) of the termite mounds. Irrespective of the termite species and the soil (control vs. IW), glucose and galactose were the most abundant sugars, representing respectively 28–44%, and 21–28% of the total amount of monosaccharides. The impact of the two termite species on the sugar content differed. For the fungus-growing termite, M. bellicosus, the total monosaccharide content in the IW was about half that of the control soil. Most of this decrease was due to the decline of glucose (34% and 14% of the total decrease) and galactose (14% and 12%) associated with the particle size of the sand (i.e. >200 µm and 50–200 µm), respectively. In contrast, the total sugar content was 4 times higher in the IW of C. niokoloensis mounds than in the control soil. At the particle-size level, this accumulation of monosaccharides was mainly due to the increase in glucose and galactose in the particle-size fractions 20–50 µm and 2–20 µm. The aggregate-size fractionation indicated that the accumulation of glucose was particularly evident in the aggregate-size fraction 20–50 µm isolated from the IW of the mounds of C. niokoloensis.