O papel subestimado do lixo de formigas cortadeiras na retenção de água no solo : uma evidência experimental

Abstract

In addition to being considered agricultural pests, leaf-cutting ants (Atta opaciceps) act as ecosystem engineers by altering the soil through, among other things, the deposition of organic material in chambers. Although previous research has shown that the refuse produced by these ants chemically enriches the soil, its impacts on water dynamics remain poorly studied. This study aimed to verify whether Atta opaciceps refuse modifies soil water retention, testing the hypothesis that its inclusion increases water retention under controlled conditions. The experiment was conducted in the laboratory using a completely randomized design with five treatments and nine replicates each. The treatments were: pure refuse (L), nest soil (SF), control soil (SC), nest soil + refuse (SFL), and control soil + refuse (SCL). All material was collected from a pasture area in the municipality of Pedro Alexandre, Bahia state, Brazil. Water retention was assessed using an adapted gravimetric method: samples were capillary-saturated for 24 hours, drained for 12 hours, weighed, oven-dried at 105°C for 24 hours, and finally weighed again. Retained water was equivalent to the difference between saturated mass and dry mass. Data were analyzed using the Kruskal-Wallis test, followed by Dunn's post-hoc test with Benjamini-Hochberg correction. A significant difference was found among treatments (χ² = 36.705; df = 4; p = 2.07×10⁻⁷). Pure refuse showed the highest retention (median = 5.87 mL), differing from most treatments, except for nest soil with refuse (SFL: 5.33 mL). Control soil showed the lowest values (2.74 mL), with no statistical difference from nest soil (SF: 3.97 mL). A gradient increase in retention was observed: SC < SF ≈ SCL < SFL ≈ L. The results corroborate the hypothesis and show that Atta opaciceps refuse acts as a modifying agent of soil physical-hydraulic characteristics. This finding expands the understanding of leaf-cutting ants as ecosystem engineers, suggesting that discarded refuse may lead to variation in water availability across the landscape and create microsites favorable for plant growth. Future field studies are needed to determine the ecological significance of this effect and its feasibility for use in degraded area restoration strategies.