Investigating the allelopathic effects of pale swallowwort (Cynanchum rossicum) on the growth success of common milkweed (Asclepias syriaca) and pale swallowwort

Abstract

Invasive species seriously threaten both biodiversity and ecosystem functionality. One mechanism that makes invasive plants successful is allelopathy, which is the release of chemical compounds that have negative effects on other plants. A vine that is native to the Ukraine region and is now highly invasive in Western New York is Pale swallowwort (Cynanchum rossicum). It has the capability to change the growth situation in favor of itself by releasing allelochemicals into the soil. Thus far, little research has been conducted to examine the direct effects of swallowwort allelopathy on the growth of native plants. To accomplish this, two types of soil from two local sites were collected; the first that contained swallowwort remains, and the second that did not contain any swallowwort. The native and confamilial species Asclepias syriaca (common milkweed) and swallowwort were planted in these soil types where growth was compared. It was hypothesized that the growth of milkweed would be limited by the swallowwort soil due to allelopathy and that swallowwort growing in soil containing remains of swallowwort would thrive. Analysis of growth data indicated that there were no significant differences in the success of swallowwort growing in both soil types and that milkweed growing in swallowwort soil was significantly smaller than milkweed planted in the control for one of two sites. This suggested that allelopathy or other changes to the soil induced by swallowwort may affect the growth of milkweed and improve the overall competitive ability of swallowwort.