Nest refuse of leaf-cutting ants mineralize faster than leaf fragments: Results from a field experiment in Northeast Brazil

Leaf-cutting ants are responsible for carrying out an important ecological process in neotropical ecosystems: the cycling of elements. However, although several studies have demonstrated the accumulation of organic matter inside colonies, little is known about the dynamics of nutrients and its residence time in nest refuse compared to the leaf material harvested by ants. This study compares the nutrient content of nest refuse and leaf material of the leaf-cutting ant Atta sexdens during states of decomposition in a transitional environment between forest and shrub vegetation in Northeastern Brazil. The decomposition rate of the refuse material was two-fold faster than the substrate harvested. In addition, there was a substantial difference in chemical and structural characteristics between both substrates. Refuse material showed higher contents of Ca whereas leaf fragments had a higher P content, more organic carbon (OC), and a higher lignin/cellulose ratio. During the period of decomposition in the field, only OC content decreased simultaneously in both substrates, indicating that changes had occurred mainly in the structure of the substrates with a low transference rate of most nutrients to the surrounding soil. A higher lignin/cellulose ratio in the leaf material may explain the higher residence time of this substrate in the environment. Results indicate that colonies of A. sexdens accelerate the decomposition of organic matter, perhaps due to reduced lignin-cellulose ratio. Organic carbon may be mineralized in the first days after the disposal of the refuse material into the nest chambers. (c) 2012 Elsevier B.V. All rights reserved.