The role of genetic variation and allelopathy in competitive effects of Ailanthus altissima on Liriodendron tulipifera

Background/Question/Methods

Invasive plant species are a widespread issue that threaten native ecosystems. A native to China, Ailanthus altissima (Tree-of-Heaven) is an aggressive, invasive tree that forms dense monotypic stands, reducing biodiversity in the areas it invades. Currently, researchers hypothesize that A. altissima out competes surrounding native species for resources and may utilize mechanisms such as allelopathy to aid this process. Multiple introductions of A. altissima could have resulted in genotypes being established that vary in competitive or allelopathic abilities. In this study, a short-term competition experiment was performed with A. altissima and Liriodendron tulipifera (Tulip Poplar). We varied both frequency and density in pots, and added activated carbon to half of the pots in each treatment to determine whether the outcome of competition would be altered by the absorption of exudates released by A. altissima into the soil. Additionally, five maternal sources of A. altissima were collected from Ohio and West Virginia to determine if genetic variation altered competitive or allelopathic ability.

Results/Conclusions

Activated carbon did not alter the competitive outcome between the two plant species, suggesting that allelopathy may not have been a major contributor to the competitive effect of A. altissima on L. tulipifera. Also, there was no indication of genetic variation between source populations in competitive ability of A. altissima. A strong negative competitive effect of A. altissima on the biomass of L. tulipifera was observed with respect to the effect of intraspecific competition on L. tulipifera (1-way ANOVA, competitor identity main effect, p<0.0001). Despite strong evidence for allelopathy in lab and grafting experiments, A. altissima’s competitive effect on L. tulipifera does not appear to rely on allelochemicals. While genetic variation in competitive ability was not found in this study, using a greater number of genotypes sampled across a larger range might have yielded different results. This research increases the understanding the role of a specific mechanism in the competitive ability of A. altissima, and how competition could impact a co-occurring native species.