Abstract
ABSTRACTThe 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.
Highlights
Riparian detritus is the primary energy source for aquatic food webs, serving as both a substrate for biological activities, such as colonization, and as a food source for microbes and invertebrates (Meehan et al 1977; Webster and Benfield 1986; Cummins et al 1989)
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
There was a significant difference in average assemblage composition at the genus level across sites (PERMANOVA, p = 0.001) indicated by a shift along the first ordination axis of the Shady Nook Boat Ramp and Power Plant sites from the Sunbury Boat Ramp and a shift along the second ordination axis of the Shady Nook Boat Ramp from the Power Plant site (Figure 1)
Summary
Riparian detritus is the primary energy source for aquatic food webs, serving as both a substrate for biological activities, such as colonization, and as a food source for microbes and invertebrates (Meehan et al 1977; Webster and Benfield 1986; Cummins et al 1989). Fundamental ecological processes of aquatic systems such as nutrient cycling, nutrient availability and organic matter production depend on the breakdown of plant litter (Webster and Benfield 1986; Bottollier-Curtet et al 2011). 60%–70% of detrital inputs (leaves, needles, bark, twigs) are retained in a stream long enough to be colonized by microbes and used as a food source for invertebrates (Meehan et al 1977).
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