Ecosystems Taxonomy & Evolution

Phenotypic plasticity to nutrient availability in a wetland invasive species

Are triploid Butomus umbellatus plants more plastic to nutrient availability than diploid plants and does this make them more invasive?

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The ability of plants to withstand and respond to a wide range of environmental conditions, termed phenotypic plasticity, is helpful in explaining the success of some invasive species during establishment, as well as their subsequent spread to new areas. Evolutionary processes also occur during plant invasions that can produce genetic changes and generate meaningful differences in invasiveness among individuals of a population. Increases in chromosome number (ploidy) have been proposed several times as being particularly important to the success of invasive plants.

Phenotypic plasticity has been found to vary among plants of varying ploidy levels. Yet, despite considerable interest in evolutionary processes occurring during plant invasions, and the potential management benefits of better understanding relationships between invasion genetics and phenotypic plasticity, the interplay between genetic variation within invading populations and nutrient response has not been sufficiently studied. For instance, the ways in which ploidy, plasticity, and available N or P interact are unknown for most species despite the potential to explain spread and impacts by invaders with multiple introduced lineages.

Triploid (left) and diploid (right) Butomus umbellatus plants growing in the glasshouse at the U.S. Army Engineer Research and Development Center in Vicksburg, Mississippi, USA. Image credit: Harms et al.

In their recent work published in AoBP, Harms et al. undertook a greenhouse study of the wetland invader flowering rush (Butomus umbellatus) to determine whether the ploidy of introduced populations explained differences in biomass production and allocation, and chemical responses to increased nitrogen or phosphorus availability. Flowering rush is a perennial Eurasian wetland plant species, with diploid and triploid cytotypes. It has been introduced into North America multiple times during the last 100 years and due to its ability to reproduce clonally has become problematic noxious weed across most of the northern United States. Across its native range most populations of the species are thought to be triploid, however in North America the diploid populations are most common. The authors hypothesized that triploid plants would have a higher phenotypic plasticity to availability of nitrogen and phosphorus than diploid plants.

Harms et al. found that, contrary to their hypotheses, triploid B. umbellatus plants were less plastic to variation in nitrogen or phosphorus availability than diploid B. umbellatus in most measured traits. Diploid plants produced more biomass than triploids under all treatments but allocation to roots was higher in triploid plants. The results of this study highlight the differences in nutrient response between cytotypes of a widespread invader of North American wetland ecosystems. They highlight that an increase in ploidy is not the only key to the invasive success of this species. The authors suggest that additional field studies be conducted to better understand the interaction of nutrients and ploidy during invasion and to help identify effective management approaches.

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