Competition among native and invasive Phragmites australis populations: An experimental test of the effects of invasion status, genome size, and ploidy level

Abstract

Among the traits whose relevance for plant invasions has recently been suggested are genome size (the amount of nuclear DNA) and ploidy level. So far, research on the role of genome size in invasiveness has been mostly based on indirect evidence by comparing species with different genome sizes, but how karyological traits influence competition at the intraspecific level remains unknown. We addressed these questions in a common‐garden experiment evaluating the outcome of direct intraspecific competition among 20 populations of Phragmites australis, represented by clones collected in North America and Europe, and differing in their status (native and invasive), genome size (small and large), and ploidy levels (tetraploid, hexaploid, or octoploid). Each clone was planted in competition with one of the others in all possible combinations with three replicates in 45‐L pots. Upon harvest, the identity of 21 shoots sampled per pot was revealed by flow cytometry and DNA analysis. Differences in performance were examined using relative proportions of shoots of each clone, ratios of their aboveground biomass, and relative yield total (RYT). The performance of the clones in competition primarily depended on the clone status (native vs. invasive). Measured in terms of shoot number or aboveground biomass, the strongest signal observed was that North American native clones always lost in competition to the other two groups. In addition, North American native clones were suppressed by European natives to a similar degree as by North American invasives. North American invasive clones had the largest average shoot biomass, but only by a limited, nonsignificant difference due to genome size. There was no effect of ploidy on competition. Since the North American invaders of European origin are able to outcompete the native North American clones, we suggest that their high competitiveness acts as an important driver in the early stages of their invasion.

Plant genome size influences stress tolerance of invasive and native plants via plasticity

“…We focused on the native and invasive lineages of P. australis in North America because they grow sympatrically in many places and have demonstrated intraspecific genome size diversity both within and between lineages (Pyšek et al 2018, 2020). Because a previous study found trait differences for P. australis by ploidy level (Meyerson et al 2016 a ), we used only tetraploids (4x) for this study, the most common and widespread cytotype in North America, regardless of lineage.…”

Regeneration of Phragmites australis from rhizome and culm fragments

“…The measures of regeneration described above represented the response variables: regeneration ability (new culms or roots produced; yes/no), regeneration extent (weight of new culms and roots; g), time to regeneration (days), and regeneration ability over time (new culms recorded in each of the 13 sampling times; yes/no). We tested the effect of the following predictors: the phylogeographic group with each clone's membership defined based on geographic origin (NA -North America; EU -Europe) and status (NA-invasive, NA-native, EU-native); plant part (culm, rhizome); environment simulated by the treatment (water, sand surface, buried in the sand); ploidy (tetraploid, hexaploid, octoploid); genome size (the amount of nuclear DNA, see Table 1 for data and Pyšek et al 2018Pyšek et al , 2020 for details on measuring karyological characteristics); and time (days, in the analysis of regeneration ability over time) on clone regeneration. Further, we accounted for the effect of initial weight and the initial number of nodes of rhizomes and culms.…”

“…We included clones of 19 distinct populations representing three phylogenetic groups (North American invasive, North American native, and European, including the whole of Russia; Table 1). This was the same set of clones, except for one that grew too poorly to be included, that were used in our previous experiment focused on the competition among clones (Pyšek et al 2020). To simulate different scenarios that may occur for a plant fragment (propagule) in the habitat typically harbouring P. australis stands, we placed cuttings of rhizomes and culms in 6-l pots (i) in water, (ii) on the sand surface, and (iii) buried them in the sand (Fig.…”

“…Although the species is among the most studied invasive plants in terms of ecology (Chambers et al 1999, Haslam 2010, Price et al 2014, Meyerson et al 2016a, Packer et al 2017, Pyšek et al 2020), physiology (Modzder & Zieman 2010, Eller et al 2017, Pyšek et al 2019, karyology (Meyerson et al 2016b or genetics (Kettenring & Mock 2012, Lambertini 2016, little is known about its vegetative regeneration ability that is crucial for its spread, colonization of new habitats as well as recovery of disturbed populations. There is no information on culm regeneration, and little is known about how regeneration differs between the clones of different origins and what is the effect of the environment.…”

Next-gen plant clonal ecology

“…High competitive ability is another obvious mechanism of spread in native communities after introduction. Clones of Phragmites australis introduced from Europe have displaced native clones in parts of North America, and Pyšek et al (2020) show that European clones in both Europe and North America have greater competitive ability than native North American clones.…”