Nematodes, indicators of the origin of the soil used by termites to construct biostructures

SummaryIn Sahelian savannas, fungus-growing termites form biogenic structures made of soil or sheetings, on the soil surface and inside the soil, to protect themselves against heat, desiccation and predators while collecting food. The purpose of this study was to determine if analysis of the nematofauna can show differences in the way termites construct sheetings according to termite species or organic material harvested. In this study, soil nematodes, which were inactive during the experiment, were passively transported in soil pellets by termites when they built sheetings. Composition of the soil nematofauna was analyzed in sheetings produced when harvesting the four different types of different organic matter and in the soil around which these structures were produced. Three of the four organic materials were applied on soil as mulch whereas wood logs were inserted in the soil. Nematode density and diversity in sheetings produced by the three different termite species present (Ancistrotermes guineensis, Ondontotermes nilensis and Macrotermes subhyalinus) were similar in the four organic treatments except for sheetings constructed within the wood by A. guineensis. Nematode densities in sheetings were about ten-fold lower than in the 0–10 cm upper soil layer. Moreover, the composition of the nematofauna in sheetings was very different from that of the upper 10 cm, except for the sheetings built on wood. A finer comparison of the soil nematofauna in the top 7 cm of soil (separated in 0–0.25, 0.25–3.0 and 3.0–7.5 cm), and of fresh surface sheetings (produced within 24 h) showed that nematode composition of sheetings was very similar to that of the soil in the superficial strata (0–3 cm).Analysis of the nematofauna led us to conclude that the soil used by termites to construct biogenic structures when harvesting organic matter originates from soil layers as close as possible to the area where the organic resource is located. Moreover, there were no differences in the soil or the three type of surface-applied organic matter used for the three fungus-growing termites.