Photosynthetic performance of invasive Vincetoxicum species (Apocynaceae)

Authors: AVERILL, KRISTINE - Cornell University; DITOMMASO, ANTONIO - Cornell University; WHITLOW, THOMAS - Cornell University; Milbrath, Lindsey

Submitted to: Invasive Plant Science and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2016
Publication Date: 10/21/2016
Citation: Averill, K.M., Ditommaso, A., Whitlow, T.H., Milbrath, L.R. 2016. Photosynthetic performance of invasive Vincetoxicum species (Apocynaceae). Invasive Plant Science and Management. 9:171-181.

Interpretive Summary: Pale and black swallow-wort are nonnative, perennial milkweed vines that have invaded various low- to high-light habitats in the northeastern United States and southeastern Canada. To better understand how well these two species grow under different light levels, we studied their ability to use available light for photosynthesis over the season and in habitats that range from being shaded to being in full sun. Black swallow-wort is clearly a sun-adapted species, with higher photosynthesis rates under high light than pale swallow-wort, although both swallow-wort species had higher photosynthesis rates than many other plants in open field habitats. Pale and black swallow-wort had similar photosynthesis rates in the intermediate light environment of a forest edge. In forest understories (where black swallow-wort is not found), pale swallow-wort had higher photosynthesis rates than other non-woody plants. Given that seed production is also highest in high-light habitats, effective management of these species in fields should be a priority.

Technical Abstract: Vincetoxicum rossicum and V. nigrum are perennial invasive vines impacting several ecosystems in the northeastern United States and southeastern Canada, including old-fields and forest understories. The integrity of these ecosystems is threatened by these two Vincetoxicum species. In order to better define the niche requirements of these two troublesome invaders, we made photosynthesis measurements in July and September 2008 to determine the differences in photosynthetic ability between the two species and across habitats varying in light availability. We used a LI-COR 6400 gas exchange system. Photosynthetic rates for leaves of plants growing in a high light habitat (1500 micromoles per meter-squared per second photosynthetic photon flux density) were greater for V. nigrum [23 (1) micromoles per meter-squared per second] than for V. rossicum [18 (1) micromoles per meter squared per second]. However, the species did not differ in the intermediate light environment of a forest edge (18-34 % of full sunlight). Although it remains unclear whether the invasive potential in this genus is species-specific, V. nigrum is clearly a sun-adapted species and shows potential for rapid growth in intermediate light environments. V. rossicum exhibited a high degree of plasticity in its photosynthetic ability with photosynthesis rates of 7.3 (0.5) micromoles per meter-squared per second in a forest understory, values that were higher than for co-occurring herbaceous species in this habitat. Both Vincetoxicum species exhibited higher photosynthesis rates than many early successional species in old-field habitats. Given that fecundity is highest in high light habitats, our results suggest that effective management of these species in old-fields should be a priority.