Changing litter composition following the dual invasion of Amur honeysuckle and the emerald ash borer alters fungal driven decomposition in Midwestern forests

Midwestern forests are currently impacted by two prominent invaders, the emerald ash borer (EAB; Agrilus planipennis ) and Amur honeysuckle (AHS; Lonicera maackii ). The loss of ash ( Fraxinus spp.) trees due to EAB invasion can further facilitate AHS invasion, driving changes in the composition of forest leaf litter to reflect a greater portion of labile, more easily decomposed litter. To evaluate the extent to which these changes alter ecosystem function, we conducted litter bag and culture-based decomposition experiments using leaf litter from sugar maple ( Acer saccharum ), oak ( Quercus spp.), black ash ( Fraxinus nigra ), green ash ( Fraxinus pennsylvanica ), spicebush ( Lindera benzoin ) and AHS. To further understand the mechanism driving differences in decay rates, we inoculated six species of decomposing fungi separately onto both single species and multispecies (half AHS and half native species) leaf litter and measured decomposition rate, fungal growth and enzymatic activity in laboratory-based cultures. AHS leaf litter decomposed faster, had increased fungal growth, and had higher activity for carbon degrading enzymes compared to native species leaf litter. Furthermore, multispecies mixtures followed the same patterns as AHS, suggesting that the addition of AHS to leaf litter to native litter will accelerate ecosystem functions related to carbon breakdown. Consequently, forests that experience the invasion of AHS and EAB induced loss of ash are likely to have faster rates of decomposition, potentially resulting in an influx of available nutrients.