The first attempt to artificially hybridize species of Potamogeton resulted in the hybrid P. perfoliatus × P. gramineus. The morphological features, reproductive behaviour and molecular markers of the offspring of this experimental hybridization were compared with those of the parental species and natural hybrids of the same assumed parentage. A phenotype corresponding to that of the natural hybrid P. × nitens was acquired from an experimental cross between P. perfoliatus and P. gramineus. All plants, both natural and artificial, of this hybrid were consistently sterile. They showed the ITS variants of both parental taxa, which is consistent with biparental inheritance of nuclear DNA. The experimental hybrid was used to test the maternal inheritance of chloroplast DNA in Potamogeton. Sequences of a chloroplast intergenic spacer (rpl20- rps12) were identical with those of the female parent. Then, the directions of the crosses resulting in the natural hybrids were investigated. Of five natural populations of P. × nitens, P. gramineus was the maternal parent of two and P. perfoliatus of three populations. The frequency of hybridization events and rise of hybrids are discussed.
Dry calcareous grasslands are among the most species-rich and endangered ecosystems in the Central- European landscape. They are of anthropogenic origin and mainly a result of grazing by domestic animals. Due to land-use changes in the last century, particularly in the 1960s, they were often abandoned or afforested. Therefore, in 1975 long-term experiments were started in the southwestern Germany (Baden-Württemberg) to determine the effectiveness of alternative management treatments in maintaining grasslands and their species composition. The aim of this study was to assess the effect of grazing (reference management treatment), mowing once a year, mulching twice a year, mulching every second year, burning once a year and succession (abandonment) on the population structure (in terms of density, age structure, reproduction mode) and seasonal germination niche of a dwarf shrub, Helianthemum nummularium, and a herbaceous plant, Lotus corniculatus. To study the age structure, annual ring analyses were applied. The classification of the reproduction mode, either by seed or vegetatively, was carried out by differentiating the central under-ground organ either as a root (in this case the individual has established from seed) or rhizome (the individual has developed from clonal multiplication). The seasonal germination niche was derived from the age structure. Management clearly affected population density and age structure. Highest density of individuals was found in the grazing and the lowest in the succession treatment. In the mulching every second year and succession treatments populations were senescent. Management also affected reproduction mode in H. nummularium. Regeneration by seed was especially enhanced by mowing and burning but was inhibited by mulching twice and succession. In the latter treatments H. nummularium reproduced only clonally. Helianthemum nummularium germinated mainly in autumn but burning by breaking the dormancy of seeds initiated germination in spring. A similar pattern was detected in L. corniculatus: burning increased germination rate in spring. Comparing population characters (density, age, reproduction mode) to the traditionally used grazing treatment, mowing was most similar and for L. corniculatus additionally burning. This is in contrast to the assessment of the vegetation of the management treatments where mowing and mulching twice per year maintain a similar floristic composition. Finally, the analysis of the population structure revealed important mechanisms behind population and vegetation dynamics.
Plants’ abilities to function are difficult to evaluate directly in the field. Therefore, a number of attempts have been made to determine easily measurable surrogates – plant functional traits (PFTs). In particular, the value of PFTs as tools for predicting vegetation responses to management (i.e., grazing and mowing) is the focus of a large number of studies. However, recent studies using PFTs to predict the effect of pasture management in different regions did not give consistent predictions for the same set of PFTs. This lead to the suggestion that more specific traits better suited for a specific region be used in the future. We consider the identification of the most adaptative traits for surviving grazing and mowing in different biomes an important goal. Using temperate grasslands in Europe as an example, we show that (i) plant height, often considered as the best predictor of species response to grassland management, is coupled with other more relevant functional traits, and that (ii) clonal traits have important, often neglected functions in the response of species to grassland management. We conclude that single traits cannot be the only basis for predicting vegetation changes under pasture management and, therefore, a functional analysis of the trade-off between key traits is needed.