1. The lack of consistent differences between the traits of native and non-native plant species makes it difficult to make general predictions about the ecological impact of invasive plants; however, the increasing number of non-native plants in many habitats makes the assessment of the impact of each individual species impracticable. General knowledge about how specific plant traits are linked to their effects on communities or ecosystems may be more useful for predicting the effect of plant invasions. Specifically, we hypothesised that higher carbon-to-nitrogen ratio (C:N) and percent lignin in plant detritus would reduce the rate of development and total mass at metamorphosis of tadpoles, resulting in lower metamorph production (total fresh biomass) and amphibian species richness.
2. To test these hypotheses, we raised five species of tadpoles in mesocosms containing senescent leaves of three common native and three common non-native wetland plants that varied in C:N ratio and % lignin.
3. Leaf mass loss, total metamorph production and the number of species that metamorphosed declined as a function of increasing C:N ratio of plant leaves. Plant lignin content was not related to the production of metamorphs or the number of species that metamorphosed. The percentage of wood frog (Lithobates sylvaticus) and American toad (Anaxyrus americanus) tadpoles reaching metamorphosis declined as a function of increasing plant C:N ratio. Mean time to metamorphosis increased and mean mass at metamorphosis declined as a function of increasing plant C:N ratio. Tadpole performance and metamorph diversity and production (biomass) were similar between native and non-native plant species with similar C:N ratio in leaves. Percent lignin was not a significant predictor of tadpole performance.
4. Our results show that the impact of a plant invasion on tadpole performance could depend on differences between the quality of the detritus produced by the invading species and that of the native species it replaces. We suggest that plant community changes that lead to dominance by more recalcitrant plant species (those with higher leaf C:N ratio) may negatively affect amphibian populations.