Strategies for a successful plant invasion: the reproduction of Phragmites australis in north‐eastern North America

Abstract

Summary Knowing the relative contribution of vegetative propagation and sexual reproduction to the dispersal and establishment of exotic plants is crucial for devising efficient control strategies. This is particularly true for the common reed (Phragmites australis), one of the most invasive species in North America. For the first time, we combined in situ field observations and genetic evidence, based on two genotyping techniques, that is microsatellite markers (SSR) and genotyping by sequencing (GBS), to determine the propagation strategies of this invader at its northern distribution limit in North America and especially in roadside ditches. Field observations revealed that, in a region where the common reed is already abundant, both seeds and plant fragments contributed to the establishment of new populations. Newly established individuals originated mostly (84%) from seeds rather than fragments, but a larger proportion of individuals originating from fragments survived the second year compared to seedlings. High genetic diversity among marsh and roadside common reed stands indicated the prime role of sexual reproduction for dispersal. The vast majority of genotypes were found in only one stand; such high genetic variability can only be explained by sexual reproduction. Half the surveyed stands comprised a single clone, suggesting that local expansion mainly occurred vegetatively. As the small proportion of SSR genotypes initially thought to be common between distant stands proved to be distinct (as revealed by GBS data), it is likely that all the stands examined were initially founded by genetically distinct individuals. Synthesis. Our study suggests that long‐distance dispersal by seeds is important for the common reed, in marshes and roadsides, while both seeds and plant fragments contribute to short‐distance dispersal along roads, at least in regions where the species is already abundant. The success of this invader in North America seems to be attributable to a reproduction strategy combining the advantages of sexuality with those of vegetative propagation. Moreover, this study shows that the GBS approach strongly reduces uncertainties associated with the use of a limited number of markers. This approach is especially valuable for ecologists dealing with an ever‐increasing number of invaders, of which few have identified microsatellite markers.

Management of invasive Phragmites australis in the Adirondacks: a cautionary tale about prospects of eradication

“…Seed set is variable and not all stems or even populations produce viable seed each year. But in addition to rhizome expansion and fragment transport, seeds, which are dispersed by wind, water, and adhesion to waterfowl throughout the fall and winter, are now recognized as important in dispersal and colonization of new habitats (Baldwin et al 2010;McCormick et al 2010;Albert et al 2015;Galatowitsch et al 2016;Kettenring et al 2016).…”

Genetic and epigenetic changes during the invasion of a cosmopolitan species (Phragmites australis)

“…Unlike many invasive clonal species spreading mostly by vegetative reproduction (Gao, Geng, Li, Chen, & Yang, 2010; Lambertini et al., 2010; Richards et al., 2012), the invasion of P. australis in North America contributes to a reproduction strategy combining sexual and vegetative propagation (Albert, Brisson, Belzile, Turgeon, & Lavoie, 2015; McCormick, Kettenring, Baron, & Whigham, 2010). The high genetic diversity in P. australis makes it more difficult to detect the epigenetic changes during the invasion.…”

Life on the edge: reproductive mode and rate of invasive Phragmites australis patch expansion

“…Sexual reproduction and spread likely plays an important role in Phragmites colonization into disturbed habitats across its North American invasion (Belzile et al 2010;McCormick et al 2010a, b;Kirk et al 2011;Kettenring and Mock 2012;Albert et al 2015). Colonization of new areas by seed is likely episodic, coinciding with disturbance to matrix vegetation and hydrologic drawdowns resulting in exposed mudflats (ter Heerdt and Drost 1994;Clevering and Lissner 1999;Alvarez et al 2005;Wilcox 2012) because flooding greatly reduces seedling emergence and growth (Weisner et al 1993;Armstrong et al 1999;Mauchamp et al 2001;Chambers et al 2003;Baldwin et al 2010).…”

“…Seeds colonizing patch edges may also contribute to a more rapid patch expansion than vegetative spread based simply on dispersal potential (Grace 1993;Silvertown 2008). However, seedlings may be less vigorous and have lower survival rates than rhizome or stolon shoots (Albert et al 2015), and may not compete well initially with vegetatively spreading clones. A wide array of studies have previously estimated the rate of Phragmites patch expansion both in its native European range and as an invader in North America (e.g., Rice and Rooth 2000;Warren et al 2001;Havens et al 2003;Lathrop et al 2003;Wilcox et al 2003;Alvarez et al 2005;Hudon et al 2005;Philipp and Field 2005;MaheuGiroux and de Blois 2007;Howard and Turluck 2013;e.g., Altartouri et al 2014;Bhattarai and Cronin 2014).…”