Quantifying the effects of Japanese knotweed (Fallopia japonica) allelopathy on native plant growth.

Abstract

Biological invasions are one of the leading causes of decreasing biodiversity around the world. Japanese knotweed (Fallopia japonica) is an invasive perennial herb native to east Asia that has become increasingly abundant in New York state. One way that invasive plants such as Japanese knotweed interfere with native communities is through the release of allelochemicals, which are secondary compounds that inhibit the growth of competitors. While knotweed is known to produce several potentially allelopathic compounds, their isolated effects on native plant growth are understudied. I performed a manipulative growth experiment treating three native species with knotweed leachate or tap water and potting them in control soil or knotweed soil collected from beneath a local knotweed population. Native species were grown for eight weeks, and their growth among treatments compared. I hypothesized that the growth of natives receiving knotweed leachate and natives potted in knotweed soil would be limited by allelochemicals. Contrary to my hypothesis, there were no significant differences between leachate and control plants. When significant results were found, plants potted in knotweed soil grew better than control plants. This may be due to increased nutrient availability or changes in soil biota caused by knotweed. My results suggest that Japanese knotweed allelopathy plays a minimal role in the species’ success and its allelochemicals are not a major concern for restoring native communities.