Population genetics of genus Puccinellia in Central Europe

Halophytic plants require or can tolerate increased levels of dissolved salts in the soil. This gives them a significant advantage in salt-rich habitats where other plant species cannot survive. Halophytes are not only found in coastal salt marshes, but also in inland saline habitats where evapotranspiration exceeds precipitation and salt-rich groundwater is transported to the surface. In Europe, inland saline habitats have been largely destroyed and, therefore, many of their halophytic species are endangered. Some halophytic species, however, are spreading along salt- treated roads. Although this might be considered positive from a conservation viewpoint (increased populations sizes of threatened species), the opposite is actually the case. As inland saline habitats are usually geographically strongly isolated harbouring unique gene pools of the locally established species, invasion of alien genetic material (i.e., from other populations of the same species) to these localities can pose a serious threat to the local populations via "genetic contamination", i.e., introduction of potentially maladapted alleles. Consequently, introduction of alien genotypes (cryptic invasions) via the roadside network is, apart from habitat destruction, one of the major threats for natural halophytic communities. Still, nothing is known about the origin and migration history of roadside populations. The aim of this study is to reveal genetic structure and migration patterns of the most widespread halophytic genus in Central Europe, the grass genus Puccinellia. Members of this genus have experienced dramatic expansion along roadsides in most European countries. They frequently form monodominant stands in narrow strips at road verges along many kilometers. Puccinellia is an excellent model system to study the impact of alien genotypes of local threatened populations, because there are numerous contact zones between presumably invading and native lineages. We apply a combination of molecular methods (RAD sequencing), flow cytometry and morphometric analyses, allowing us (i) to assess the impact of cryptic invasions on the structure and diversity of halophytic communities in the current European landscape, and (ii) to resolve the challenging taxonomy of this group in Europe. The results will be directly applicable to conservation of rare inland populations of Puccinellia and associated communities.

Halophytes-salt-tolerant plants that grow in soil or waters of high salinity-are of a great conservation concern due to the scarcity of saline habitats in Central Europe. These habitats have been vastly destroyed during the 20th century and their still surviving remnants are highly fragmented. Even the existing localities are threatened by ecological succession, changes in the water regime, or undesirable industrial activities. As much as halophytic species are rare in natural habitats, some of them are common in artificial habitats. Some species tend to spread heavily along the verges of salt-treated roads, travelling along the road net across the entire continent. The most common such species is the weeping alkaligrass (Puccinellia distans). It is widespread in Europe where it frequently forms monodominant communities in narrow strips along road verges. The origin of the expanding roadside populations, however, has not been investigated so far. It is possible that the plants spreading along road verges may have arrived from distant regions and thus represent an alien genetic material in the regions they are spreading into. Invasions of alien genotypes into indigenous populations of the same species (so called cryptic invasions) have been, unlike invasions of alien species, largely overlooked. The impact of cryptic invasions on the biodiversity of plant communities can, however, be significant and can include genetic pollution of indigenous genotypes, which is a clearly negative phenomenon for nature conservation. The expansion of Puccinellia distans therefore poses a potential threat for Central European inland halophytic communities, and especially for native populations of this species, if the spreading roadside plants indeed invade natural habitats and hybridize with the native genotypes. The goal of this project was to access the risk of such a cryptic invasion of Puccinellia distans in Central Europe. By a combination of flow cytometry and genetic methods, we showed that there is indeed one lineage of Puccinellia distans that is nearly exclusively spreading along roadsides and in other artificial habitats. Other found lineages were rare and mostly confined to natural habitats. Two rare isolated lineages were found in the saline habitats in Central Germany and in the localities of mud volcanoes in Northern Italy. Other rare lineages occurred in the Pannonian Basin, restricted to Austria, Slovakia, Hungary, and Romania only. The roadside lineage was found spreading to these natural habitats and an indirect evidence of its hybridization with some of the native lineages was found. Although more studies are needed on this topic, the existing results clearly raise the awareness about the thread of cryptic invasion followed by hybridization and potential genetic erosion of the native lineages.