Leaf Litter Leachate Limits Fungal Pathogen Growth but Not Amphibian Infection

Terrestrial leaf litter can release chemical compounds into the water, creating a solution called "leachate" that can have direct and indirect impacts on freshwater organisms. In this study, we investigated the direct effects of leaf litter leachates from six plant species on the fungal pathogen, Batrachochytrium dendrobatidis (Bd) in vitro, and their effects on tadpole infection in vivo, when tadpoles were reared in leachates before Bd exposure. In our in vitro experiment, all six types of leachates reduced the concentration of Bd zoosporangia, and there were mixed effects of leachate type on the concentration of Bd zoospores. Purple loosestrife leachate had the greatest effect on Bd in the in vitro experiment suggesting that this plant species may produce chemicals that are directly detrimental to Bd. The negative effects of leachates on Bd in vitro increased with leachate concentration. In our in vivo tadpole experiments, leachates had no measurable impact on the tadpole host survival, size, development, or infection with Bd. Our results indicate that leaf litter leachate can have direct negative effects on Bd, but these effects may not translate to large changes in infection in tadpoles. However, future studies are necessary to determine the comprehensive impact of leachates on aquatic amphibians and their pathogens in natural populations. These results highlight the importance of understanding terrestrial inputs into freshwater systems.