Zdenka Hroudová

Ecology of two cytotypes ofButomus umbellatus II. Reproduction, growth and biomass production

Generative and vegetative reproduction of diploid and triploidButomus umbellatus L., and growth and biomass production of both cytotypes under two different nutrient levels were compared.Seedling survival was studied under controlled conditions in a growth chamber; the response of plants to different nutrient conditions was studied in experimental garden.Both cytotypes do not differ in seed germination and seedling survival. Triploids produce more aboveground and underground biomass, more numerous lateral rhizome buds, and have significantly higher flowering stalks. Low generative reproduction (limited seed production) in triploids is compensated for by more intensive vegetative reproduction. High nutrient level appeared to be stressful for plants of both cytotypes: it limits plant growth and causes plant mortality. Triploids are more viable than diploids in this case, which may be important for their survival under conditions of high trophic level.

The biology of Butomus umbellatus in shallow waters with fluctuating water level

Butomus umbellatus L. is a plant species typical of littoral communities of river and stream shores. It can form continuous stands in shallow reservoirs with fluctuating water level. Their expansion is promoted by: (a) intensive vegetative reproduction of plants, (b) crowded sprouting from rhizome fragments on emerged pond bottom, (c) shallow water layer in the year following summer drainage. Expansion of B. umbellatus depends on ploidy level: two cytotypes were found in the Czech and Slovak Republics, differing in their reproductive ability. Seed production of triploids is strongly limited (they are self-incompatible within clones), while diploids can be fully fertile. Nevertheless, even in diploids, the efficiency of seed reproduction under natural conditions is low. Triploids spread by intensive vegetative reproduction, which is decisive for clonal growth of populations and their regeneration after scraping of bottom surface. During seasonal development, maximum of aboveground biomass is produced in early summer, while underground biomass increases till autumn. Growth of the plants is limited by cutting before maximum underground biomass is attained, or by duck grazing.

Effect of anatomical structure on the buoyancy of achenes of two subspecies ofBolboschoenus maritimus

Differences between two subspecies ofBolboschoenus maritimus (L.)Palla (=Scirpus maritimus L.) in different habitats (littoral and terrestrial) are partly due to variations in the buoyancy of their achenes, caused by different anatomical structure of the fruits. This hypothesis was tested by comparing fruit buoyancy and anatomy of both subspecies at several localities.Plants were sampled fromBolboschoenus maritimus subsp.maritimus (plants with branched inflorescences and triangular fruits, 4 localities) andB. maritimus subsp.compactus (Hoffm.)Hejný (plants with compact inflorescences and prevailing concave fruits, 4 localities) in the Czech and Slovak Republics, andB. maritimus subsp.compactus (plants with compact inflorescences and convex fruits, 1 locality) from the coast of South Sweden. From each locality a plant with several tubers connected by rhizomes was taken and transferred into the experimental garden; from these cultivated plants (clones) mixed samples of fruits collected from each clone were used for buoyancy tests and a study of their anatomy.Fruit buoyancy was found to depend on the anatomical structure of the pericarp—the presence of aeriferous tissue in the exocarp serves as the main floating organ. This differentiated all plants studied into two groups: short-floating subsp.maritimus, with a thin or none acriferous tissue in the exocarp, and long-floating subsp.compactus with well developed aeriferous tissue. Differences in fruit buoyancy corresponds to differences in the prevailing habitat types of both subspecies studied in the inland sites: the frequent occurrence of subsp.compactus in temporarily flooded terrestrial habitats contrasts with the prevalence of subsp.maritimus in the littoral of water bodies. This is an example of intra-specific ecological differentiation leading to differentiation in wetland communities.

Ecological differentiation of Central EuropeanBolboschoenus taxa and their relationship to plant communities

The taxa of theBolboschoenus maritimus group occurring in Central Europe were studied with respect to morphological differentiation, plant communities and soil conditions. Four morphological types ofBolboschoenus were distinguished, differing in habitat conditions, dispersal and distribution: type 1 —Bolboschoenus maritimus subsp.maritimus with narrow triangular fruits; type 2 —B. maritimus subsp.maritimus with wider triangular fruits, type 3 —B. maritimus subsp.compactus with round convex fruits; and type 4 —B. planiculmis auct. with concave fruits. Strong ecological differentiation of these types was found compared with relatively weak morphological diagnostic features. High discriminant efficiency appeared in the relationship to soil chemistry. Differences were also found in habitat-type spectra of individualBolboschoenus morphological types, which was reflected in their affinities to plant communities. Nomenclature, taxonomic classification, and distribution of these taxa in Europe need thorough revision.

Ecology of two cytotypes ofButomus umbellatus III. Distribution and habitat differentiation in the Czech and Slovak Republics

The distribution, total frequency of occurrence, regional differences and habitat conditions of diploid and triploidButomus umbellatus L. were studied in the Czech and Slovak Republics. Triploids are more frequent than diploids, with numerous localities in warm lowland regions in river floodplains. Diploids were found primarily in the South Bohemian Třeboň basin, outside the warm regions. The two cytotypes do not differ in dependence on water depth. Triploids occur more in habitats with more alkaline and base-rich soils. Considering the total distribution of both cytotypes in the area studied, triploidB. umbellatus appears to be more successful than its diploid progenitor, owing to its wider habitat range and superiority in vegetative reproduction.

Germination responses of diploid Butomus umbellatus to light, temperature and flooding

Summary The germination of seeds of diploid Butomus umbellatus was studied to determine the favourable conditions for germination and whether seed germination may represent a limitation within the sexual reproductive cycle of this cytotype. The need to stratify the seeds and the response of the seeds to environmental conditions during germination were studied. The influence of light/darkness, temperature, day length, and flooding/aerobic conditions was tested. Seed germination was enhanced in the winter by cold wet stratification, which indicates prevailing seed germination in the spring. Seeds germinated best in light, at relatively high temperatures (20°–30°C), in long days. Seeds were able to germinate when flooded; in most cases, flooding supported germination. In field habitats, the optimum conditions for the germination of B. umbellatus seeds may be found on an open emerged bottom saturated with water or under a shallow water layer. The process of germination does not represent a high-risk stage in the sexual reproduction of this cytotype of B. umbellatus . The time of germination (late spring or summer months) contributes to seedling mortality due to the competition of adult plants or other early-germinating species.

The effect of submergence on tuber production and dormancy in two subspecies ofBolboschoenus maritimus

Two subspecies ofBolboschoenus maritimus (L.)Palla were cultivated in submerged and non-submerged conditions. The production of tubers, the proportion of tubers remaining dormant and the time between production and reactivation were investigated.Total tuber production was found to be dependent on subspecies and may be considered a biological character of the subspecies.Bolboschoenus maritimus ssp.compactus, a subspecies of less, flooded habitats, produced more tubers with a greater capacity for growth leaving a smaller proportion of dormant tubers. Inactivity of tubers and their reactivation after one or two years were enhanced by submergence in both subspecies.The proportion of tubers that are permanently dormant as well as the dormancy of the whole plant are important features influencing the survival of populations ofB. maritimus over periods of unfavourable conditions.

Germination and seedling establishment inAlisma gramineum, A. plantago-aquatica andA. lanceolatum under different environmental conditions

The seed germination and seedling establishment ofAlisma gramineum, A. lanceolatum andA. plantago-aquatica were investigated to find differences in the reproductive strategy of these species and to explain their ecological and distributional differentiation. The influences of stratification, temperature and flooding on seed germination, winter survival of seedlings and their further development were tested in the laboratory and in the experimental garden.Seeds of the all species studied were dormant immediately after harvesting. Cold stratification was necessary for successful germination. Seeds germinated best under shallow water in temperatures of 25 °C and 25/10 °C and did not need fluctuating day/night temperatures to break dormancy. Seedlings established best under the limosal-terrestrial conditions in summer, and overwintered successfully only when flooded. The main interspecific differences found were in the percentage of germinative and dormant seeds, in the germination rates after individual treatments, in the course of ontogenetic development and in the longevity as well as in the resistance of vegetative organs to environmental conditions. Possible effects of the above-listed facts on the ecological amplitude and distribution of the studied species are discussed.

Vegetation dynamics in a fishpond littoral related to human impact

To determine how fishpond vegetation reflects human activities, changes of littoral vegetation of the Opatovický fishpond (South Bohemia) were studied over a period of 26 years. The littoral vegetation of this fishpond has been mapped in 1992 and 1997, and compared with a former study in 1971 together with relation to the soil chemistry of the bottom sediments. The following factors influence the vegetation dynamics: fluctuations of water level, trophic level of habitat, changes in management (mowing) and mechanical disturbances (scraping). The expansion of reed stands (Phragmites australis), disappearance of small sedge stands and a decrease in the area of Glyceria maxima stands were the main characteristics of the vegetation dynamics within the period studied; most other plant communities remained stable. In addition, successional development on scraped shores led to the re-establishment of wetland communities (positive effect) or to ruderal vegetation on islands of deposited material (negative effect). The fishpond may be characterized as meso- to slightly eutrophic and was found to be relatively resistant to the influence of local sources of pollution: the total trophic level (total N, nitrates, phosphates) did not increase at all. As the fishpond has been proposed as a nature reserve for valuable plant communities and water bird diversity, fishery management and human activities in the surrounding area need to be controlled.

Chromosome numbers within the genusBolboschoenus in Central Europe

Two chromosome numbers n=54, n=55 were found inBolboschoenus plants studied from Central Europe (Czech Republic, Slovakia, Hungary, Poland) and coastal regions of Europe (the Netherlands, Sweden). The number n=55 is typical forB. maritimus subsp.maritimus with narrow fruits and mostly also forB. maritimus subsp.compactus; the number n=54 characterizesB. planiculmis auct. The morphological type ofB. maritimus subsp.maritimus with wide fruits represents a stable taxon occurring in freshwater habitats throughout Europe. Its variation in chromosome numbers (both n=54, n=55) indicates a possible hybrid origin, probably resulting from hybridization betweenB. maritimus subsp.maritimus with narrow fruits andB. planiculmis auct. Spontaneous hybridization betweenBolboschoenus taxa in the regions with mixed populations may explain the origin of the intermediate morphological and anatomical characters of plants from some localities and the deviations in chromosome numbers.