The effect of fungus-growing ants and termites on soil carbon pools in tropical ecosystems / Ilse Lieve Ackerman.

Tese (Mestre)- Cornell University, 1999

This study models the effects of fungus-growing ants and termites on soil carbon pools in tropical ecosystems. Because of the unique biology of the fungus-growing ants (Attini) and termites (Macrotermitinae), these groups of insects play a disproportionate role in decomposition processes in the tropical ecosystems in which they occur. Data from the literature were compiled to estimate the rates at which these macrofauna groups harvest plant material and return organic matter to the ecosystem. These data were used to modify an existing model of decomposition, from the Carnegie Ames Stanford Approach (CASA), to take into account the higher litter turnover rates resulting from the activities of these organisms and their associated fungi. Using these available data, the model predicted a 22% reduction in litter microbial carbon, a 13% reduction in soil microbial carbon, and an 19% reduction in the pool of slow carbon with the activities of fungus-growing termites. The predicted effects of fungus-growing ants were slighter, a corresponding 11%, 1.5%, and 2.5% reduction in the above carbon pools. By showing where information is most sparse, the results of the literature review serve as a guide for future field data collection. in particular this study highlights the need for surveys of the densities of macrofaunal groups in order to scale up colony-based information. Meanwhile, this study provides a model which allows for simple manipulation of parameters and easy rewiring of modules as more data on macrofauna activities in the tropics becomes available. According to its current parameterization, the magnitude of the fauna-mediated transfer of organic material and the fungal-mediated increase in rate of organic matter decomposition is sufficient to cause appreciable changes in soil carbon stocks in sites in which these faunal groups occur. Models of carbon cycling applied accross both temperate and tropical ecosystems could improve by taking into account these biological differences in decompoistion rates.