Physico-chemical typology of the biogenic structures of termites and earthworms: a comparative analysis

A comparative analysis of 14 physico-chemical and organic parameters was conducted on three types of biogenic structures: earthworm casts and crop sheetings built by two fungus-growing termites (Ancistrotermes guineensis and Odontotermes nilensis) and compared to the neighbouring soil in a mango orchard in the Thiès region of Senegal. A principal component analysis shows clearly that the biogenic structures were differentiated from the neigbhouring soils in their content of organic components. The amino sugar contents of biogenic structures were 3-5 times higher than those measured in soil. In these structures, an increase in the contents of phenols and proteins was also observed. In contrast, their physical and chemical characteristics (texture, cationic exchanges capacity) were little different from those of the soil with the exception of their much lower water-retention capacity. Differences were also noted between the biogenic structures: the structures built by the two species of termite show more similarities with each other than with the casts. This result was confirmed by a similarity dendrogram which was used to graduate oppositions between samples. Casts were different from termite sheetings primarily in their C and N contents which were twice as high. Conversely, the contents of proteins in termite sheetings were higher than those measured in casts. Altogether, the results suggest that, in the biogenic structures, the organic content is stored and protected from mineralization.