Soil micromorphology and CO2 exchange in initial Atta sexdens (Hymenoptera: Formicidae) nests

Abstract

Ants build underground nests to protect their colonies and to improve conditions for their offspring. The excavation of nests, by ants, modifies the soil structure, facilitating gas exchange and circulation, which needs further studies. Do initial nests modify the initial chamber soil matrix and gas exchange? The objective was to study the soil micromorphology of the wall of the chamber of initial nests of the leaf-cutting ant A. sexdens and how the CO2 diffuses into the soil matrix. The CO2 concentration in initial four-month-old A. sexdens nests was measured for 24 h using a respirometric system with a gas meter and closed nest holes (obliterated). After this period, they were opened and the CO2 concentration measured again. In addition, 15 cm deep holes were drilled into the ground 15 and 60 cm away from the ant nest hole. The CO2 was measured in these orifices and then they were sealed for 24 h and new ones made after this period. The contents of the nest chambers were removed, after the CO2 measures and the soil micromorphology of the walls of the initial chamber analyzed. The CO2 concentration in the nest chamber was greater than that in the soil at 15 and 60 cm distant from it. The CO2 accumulation did not increase with the obliteration of the nest entrance for 24 h. Coarse material, mainly quartz and charcoal fragments, besides fine material of clay, organic matter and iron oxides composed the soil of the wall of initial nests. The soil porosity in the chamber walls of the initial nests was lower than that of the matrix of the adjacent soil and differed between those of the nests. Initial nests of A. sexdens modifies the soil matrix of their walls, allowing to CO2 exchange between its chamber and adjacent soil.