Population and genotype-level effects on light responses in an invasive liana, celastrus orbiculatus (Oriental Bittersweet)

Background/Question/Methods   Invasive exotic plants are associated with homogenization and reduction of community biodiversity, and the quantity and density of these harmful non-natives is increasing worldwide. Many factors affect plants' invasibility, including features of the novel community and of the plant itself. Exotic plants with greater genetic diversity or phenotypic plasticity are likely to be more successful invaders, especially under shifting environmental conditions. Celastrus orbiculatus (oriental bittersweet) is a non-native liana whose density has reached invasive proportions in parts of North America. Previous research tested bittersweet seedlings growth under a range of light conditions and found significant differences among light treatments in a common garden experiment. Our goal was to examine the effects of light on growth of Celastrus orbiculatus from three different Western North Carolina populations. Predications were that genotypes would respond differently to varying light conditions and that some populations would be more plastic than others. We used a common garden experiment to test the growth of different bittersweet populations and genotypes under various light environments.

Results/Conclusions   In the common garden experiment, all populations responded differently to light conditions (P = 0.0176). Also, differences in bittersweet populations' performance (biomass gain) and plasticity were identified (P < 0.0001), and these growth responses might be attributable to genetic causes. Genotypes from one site, which performed best under all light treatments (P = 0.0001), could have been adapted to this wide range of conditions; their site of origin is an experimental forest with ongoing timber harvests and multiple canopy gaps. We are now using controlled environments for further tests of phenotypic variation, using seeds to avoid potential effects of canalization. We are also using AFLPs to examine population genetic structure across cohorts, as this might give insight into the evolutionary forces affecting patterns of spread in Celastrus orbiculatus.