Azteca ants connect aboveground and belowground processes in a wet tropical forest

Ecosystem function in terrestrial systems often depends on linkages between aboveground and belowground processes. Aboveground-belowground links can have disproportionate impacts on ecosystem function if nutrients produced or released in one subsystem (e.g., labile carbon through photosynthesis) limit productivity in the other. Organisms that amplify such linkages are thus important research foci. Here, we report a study conducted on Barro Colorado Island in Panama in which we tested whether refuse generated from the ant Azteca trigona affects decomposition rates and arthropod community structure. We predicted that 1) decomposition rates would be faster under Azteca nests, 2) this accelerated decomposition would be caused by refuse addition, and 3) chemically distinct leaves would respond differently to refuse addition. We found support for the first prediction using an observational study, which showed that cellulose and wood decomposition rates were significantly higher under Azteca nests than in locations 10m away. We found support for the second prediction in an experimental study in which we added either refuse, soil, or nothing to randomly selected forest plots over the course of six weeks, and measured the effect of these treatments on decomposition. We found that the addition of refuse (but not soil) significantly increased decomposition rates of both cellulose and wood by as much as 75% after 4 weeks. Refuse addition increased arthropod abundance and changed the community structure. Given the magnitude and scope of their impact, our results suggest that Azteca ants may be an important connector of ecosystem processes in this system.