Effects of log-nesting ants on wood-decay fungi and forest decomposition

Many ant species commonly use fallen logs as nesting sites for their colonies. However, although the presence of antimicrobial adaptations in ants is well established, the effects of these insects on wood decay fungi and the decomposition of coarse woody debris is unknown. We tested the null hypothesis that ants do not affect fungal growth using the ant Aphaenogaster rudis, a common log-nesting species and keystone seed disperser in eastern deciduous forests. Live worker ants were surface-sterilized in the laboratory and placed in two different densities onto media plates inoculated with the white-rot fungus Pleurotus ostreatus (Pleurotaceae). We found that mycelial growth rates in the presence of ants at either density treatment were significantly slower relative to ant-free controls. We then conducted additional tests using inoculated wood samples as an arena to explore the effects of ants on wood-rot fungi and decomposition in a more ecologically applicable environment. This study suggests that ants may have hitherto overlooked effects on the ecology of wood-rotting fungi, and offers new implications for the role of ants in forest decomposition and nutrient exchange.