Variation in Japanese Knotweed Populations (2023)

Undergraduate: Ashley Behringer

Faculty Advisor: Stacy Endriss
Department: UNCW Environmental Science

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Japanese Knotweed (both Japanese Knotweed and the hybrid, Bohemian Knotweed) are invasive plants with diverse negative impacts, including harm to native species and infrastructures. We investigated whether Japanese Knotweed expressed predictable variation along environmental gradients and across ploidy levels by measuring resistance to herbivory across scales of environmental variation: climate and soil type. Understanding the variation among populations helps with management strategies. Plants were propagated from 5 rhizomes collected from 50 populations along the eastern US. After plants were established in pots for 4 years, 3 young leaves were photographed in the summer. We predicted that Japanese Knotweed populations have locally adapted and that both ploidy and abiotic environmental gradients are key drivers of variation between populations. We proposed that (1) leaves would be plumper the colder and drier the origin of the Japanese Knotweed population and (2) populations from areas with more sediment clay composition would experience greater herbivory. We found that ploidy was a strong driver in the variation of leaf size (P < 0.001) and shape (P < 0.01). The leaf blade area (not plumpness) increased with latitude, showing local adaptation amongst some populations. The soil composition did not impact insect herbivory, but did influence plumpness and blade area of the leaf. Further, we confirmed using leaf morphology to help identify ploidy levels of plants provided numerical guidelines to assist with identification. While controlling the spread of this invasive plant is difficult, these findings will assist in understanding the variations of different populations to create management plans.

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