Effects of ant bioturbation and foraging activities on soil mechanical properties and stability

Ants are ecosystem engineers, and their nesting and foraging activities are critical to modifying soil structure. In this paper, the soil physical and mechanical properties of in situ subterranean ant nesting soil and non-ant nesting soil around the nest of the Iridomyrmex anceps were investigated so as to evaluate the effects of activities such as nest building and foraging on soil hydrologic and stability. The results showed that ant activity increased the content of organic matter, total nitrogen and phosphorus in the soil, and decreased soil pH. The activities of ants altered the soil structure. The density, specific gravity and saturation of subsurface ant nesting soil and non-ant nesting soil showed highly significant differences, while the moisture content, dry density, pore ratio and porosity showed significant differences. The soil mechanical property tests results showed that the ant activity increased the compressibility of the soil. The ant activity reduces the resistance of soil against relative movement under the action of external force, as well as the strength of soil against axial pressure under the condition of no lateral restraint, whereas the residual strength is increased. Under low confining pressure conditions, ant presence had no significant effect on the ultimate strength of soil. However, the ultimate strength of ant nest soil was significantly lower than that of non-ant nest soil under condition of high confining pressure. These findings unveil that ant activities positively affect the energy cycle and species diversity in ecosystems but significantly reduce soil mechanical properties and stability.