Germination of four Central European Bolboschoenus species (B. yagara, B. koshewnikowii, B. maritimus and B. laticarpus) was studied. The need for stratification and the influence of temperature and water regime on seed germination were tested in the laboratory. Cold wet stratification in the laboratory as well aswater stratification in the field enhanced the germination of all species. Germination was facilitated by increasing stratification length, but differed between species. Field stratification in water improved the germination of all species compared to stratification in soil. Germination requirements of the four Bolboschoenus species, despite the broader ecological amplitude of B. laticarpus, were similar. The best germination occurred after four months of field stratification in cold water. All species germinated best in aerobic conditions when the day/night temperature fluctuations were high (30/10 °C). These conditions correspond to those occurring where the seedlings tend to establish themselves in the field: exposed pond bottoms or wet soil in field depressions.
This paper describes the reproductive characteristics of 93 neophytes (alien species introduced after 1500 A.D.) of the flora of the Czech Republic and compares trait values between naturalized invasive and naturalized non-invasive neophytes. Species were sampled and seed collected in the field from multiple localities in the Czech Republic. Traits related to seed production (propagule number per plant and per population), dispersal (propagule size, length/width ratio and weight; buoyancy; epizoochory; terminal velocity) and establishment (germination; seedling relative growth rate; seedling establishment) were measured for each species either in the field, in a common garden experiment or in the laboratory. Invasive species significantly differ from naturalized non-invasive species in propagule length/width ratio (by having lower ratio, i.e. more rounded propagules) and fecundity (invasive species are more fecund, both per individual plant and in terms of the population propagule production). Invasive species have proportionally fewer seedlings establishing in the autumn and better capacity for dispersal by wind than non-invasive species. The results for several traits differ depending on whether or not the effect of phylogeny is included in analytical models. Considering species relatedness expressed as a taxonomic hierarchy, invasive species have lighter propagules and higher population propagule numbers, and marginally significantly differ in producing more propagules per plant and having higher capacity for dispersal bywater.We found that most variation in invasiveness is linked to variation among species within genera. This distribution of relatedness means that predictions of whether a species will become invasive cannot be based on traits of the relatives of the given species at higher taxonomic levels. The distinction made in this paper, i.e. invasive species vs. naturalized but non-invasive species, can potentially contribute to a deeper understanding of the role of traits associated with invasiveness because the crucial transition from the naturalized to invasion stage is rarely addressed in invasion ecology.