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Plasticity in salt tolerance traits allows for invasion of novel habitat by Japanese knotweed s. l. (Fallopia japonica and F.xbohemica, Polygonaceae)¹

² Department of Ecology and Evolution, Stony Brook University, Stony Brook, New York 11794 ³ Department of Biology and Center for Genomics and Systems Biology, New York University, New York, New York 10003 ⁴ Biology Department, University of Leicester, Leicester, LE1 7RH, UK

ABSTRACT

Japanese knotweeds are among the most invasive organisms in the world. Their recent expansion into salt marsh habitat provides a unique opportunity to investigate how invasives establish in new environments. We used morphology, cytology, and AFLP genotyping to identify taxa and clonal diversity in roadside and salt marsh populations. We conducted a greenhouse study to determine the ability to tolerate salt and whether salt marsh populations are more salt tolerant than roadside populations as measured by the efficiency of PSII, leaf area, succulence, height, root-to-shoot ratio, and total biomass. Clonal diversity was extremely low with one F. japonica clone and five F. xbohemica genotypes. The two taxa were significantly different in several traits, but did not vary in biomass or plasticity of any trait. All traits were highly plastic in response to salinity, but differed significantly among genets. Despite this variation, plants from the salt marsh habitats did not perform better in the salt treatment, suggesting that they are not better adapted to tolerate salt. Instead, our data support the hypothesis that plasticity in salt tolerance traits may allow these taxa to live in saline habitats without specific adaptation to tolerate salt.

Key Words: adaptive evolution • clonal plant • Fallopia japonica (Polygonaceae) • Fallopia xbohemica • Japanese knotweed • natural hybridization • salt tolerance • succulence