Decomposition and benthic macroinvertebrate communities of exotic Japanese knotweed (Fallopia japonica) and American sycamore (Platanus occidentalus) detritus within the Susquehanna River

Abstract

The invasive shrub Japanese knotweed (Fallopia japonica) is spreading through riparian forests in Central Pennsylvania. There is concern that detritus from this species may impact adjacent aquatic ecosystems, as allocthonous material forms the basis for aquatic food webs and may impact benthic community structure. This study compares key ecosystem processes within Japanese knotweed leaf litter to leaf litter of a native riparian species, American sycamore (Platanus occidentalis). We assess benthic macroinvertebrate communities and decomposition rates within experimental Japanese knotweed and American sycamore leaf packs at three sites within the Susquehanna River. Japanese knotweed detritus hosted a similar macroinvertebrate community to American sycamore and their assemblages had similar representation of functional feeding groups. The similarity between the invertebrate communities occupying American sycamore and Japanese knotweed detritus indicates that macroinvertebrates are able to utilize non-native litter for habitat and potentially as an energy source. American sycamore decomposed at a faster rate than Japanese knotweed, lending support to the Novel Weapons Hypothesis, which suggests that non-native species like Japanese knotweed may inhibit microbial colonization and subsequent litter breakdown. Our results suggest that invasion of Japanese knotweed along riparian corridors of large river systems may not have severe ecological consequences on local ecosystem processes.