The distribution of Silicon in soil is influenced by termite bioturbation in South Indian forest soils
Résumé
Si is one of the most abundant element on earth and an abundant literature shows its beneficial effects on plant growth and resistance. We here question the influence of termites, as key soil bioturbators, on the distribution of Si in a tropical soil. The abundance and forms of Si in termite mounds build by Odontotermes obesus (TM) or in the soil eroded from TM but redistributed on the ground surface (EROD) were compared to those measured in the 0–5 (Ctrl0-5) and 70–120 cm soil layers (Ctrl70-120). Although termites use the soil from Ctrl70-120 for building their mounds, we found that TM and EROD had intermediate soil physical, chemical and mineralogical properties between Ctrl0-5 and Ctrl70-120. Clay content was not significantly different between soil materials. However, the lower variability measured in TM than in the soil suggested that termites used soil layers with higher amounts of clay fraction and with a preference especially for layers enriched in 2:1 clay minerals (smectite) most likely because they provide better physical properties in terms of plasticity and water retention than kaolinite. Finally, phytoliths and bioavailable Si (SiCC) contents were increased in TM in comparison with Ctrl70-120, suggesting an incorporation of phytoliths in termite construction through their saliva and/or an increasing availability of SiCC from the minerals. In conclusion, this study highlights how termites, through their feeding and building activities, impact Si distribution in tropical soils.
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