Why does Atta robusta (Formicidae) not change soil features around their nests as other leaf-cutting ants do?

Based on recent papers studying the effect of leaf-cutting ants on soils, we hypothesized that Atta robusta nests modify chemical properties in oligotrophic Restinga soils. We tested if the nests (i) increase mineral nutrients, organic matter, cationic exchangeable capacity, pH, and (ii) decrease aluminum saturation. Such soil variables were determined at three depths from both active A. robusta nests and control sites. Only K concentration was greater in nests but the other parameters were not significantly modified. The exception was aluminum saturation which was significantly lower in sampled nests. Low clay content is suggested as main explanation which nullifies the effects of nests. Furthermore, complexation of aluminum with organic acids from decomposition may explain its reduced saturation.