Article

Generative reproduction of long stalked pondweed (Potamogeton praelongus Wulfen) in the laboratory

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  • East Bohemian Museum in Pardubice
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Abstract

Generative reproduction of Potamogeton praelongus in the laboratory is a possible way to preserve this critically endangered species in the Czech Republic (CR) as well as the whole of central Europe and to increase the low genetic diversity of its populations. Different methods of seed storage, breaking seed dormancy, cultivation temperature, seed age and interactions of these factors were examined to determine the suitable conditions for generative reproduction of P. praelongus in the laboratory. The most suitable storage method was keeping dried seeds in paper bags and submerging them in water for one month before the test. The best results of breaking seed dormancy were gained by near-natural methods - stratification, effect of microbial activity in water, scarification. Also methods using synthetic chemical substances and multiple dormancy breaking measures were successful. Seeds germinated better at 28 ± 1 °C than at 21 ± 3 °C. The best cultivation medium was river water. The strongest interaction was found between the storage method and treatment of seeds before cultivation. Seeds stored for about one year germinated better than fresh or shortly stored (6–9 months) ones. Optimal conditions for generative reproduction of P. praelongus in the laboratory were determined to be used for preservation of this species in CR.

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... To investigate the potential role of ethylene as a germination stimulus, additional replicates of 20 seeds were prepared as previously described but imbibed in distilled water for 24 h and exposed to an 80 mg.L − 1 Ethephon (Sigma Aldrich, Germany) for a further 24 h prior to being placed in 20 mL sealed plastic tubes containing 15 mL of either acidic, neutral or alkaline germination media solution. Ethephon is known to gradually release ethylene gas in solution, and ethylene is a known a germination stimulant for many aquatic and wetland plant species (e.g., Baskin and Baskin, 2014;Cross et al., 2014Cross et al., , 2015Cross et al., , 2018bPrausová et al., 2014). Seeds were then incubated at 21 or 25 • C on a 15-h photoperiod or in constant darkness for six weeks as previously described. ...
... Previous authors have proposed that seed dormancy in U. vulgaris, at least in temperate regions, is likely alleviated by a period of cold stratification over the cold winter months prior to germination in spring, as indicated by high germination success reported for seeds incubated under indicative spring temperatures following cold stratification (Baskin et Baskin, 1998). Similar germination responses following cold stratification have been reported for species co-occurring with U. vulgaris, including Potamogeton praelongus (Prausová et al., 2013(Prausová et al., , 2014. However, data from the present study suggests that cold stratification was poorly effective at alleviating seed dormancy in U. vulgaris, and that MPD was instead alleviated by a period of warm stratification (Fig. 4). ...
... The presence of ethylene probably compensates the lack of light during germination. Positive effect of Ethephon on germination was proved for other aquatic plants, for example up to 5 % Potamogeton praelongus seeds germinated with Ethephon (Prausová et al., 2014). Germination rate was high (>75 %) in ethylene-exposed seeds incubated at 21 ºC, on a 15-h photoperiod in alkaline germination solution. ...
Article
Generative reproduction of the carnivorous aquatic plant Utricularia vulgaris (Lentibulariaceae) from seeds may be a critical process in the recovery of natural populations following temporary drying of habitat, and in the colonisation of new potential sites through dispersal of seeds by water birds. However, little is presently known about the seed ecology and germination biology of this species. We tested the germination response of seeds under various temperature and seed storage regimes, to examine the processes required for seed dormancy alleviation and the effects of different germination solution and temperature on germination probability. Seeds likely possess non-deep simple morphophysiological dormancy alleviated by warm stratification. Highest germination success was recorded for warm-stratified seeds and seeds exposed to ethylene. Seeds were photophilous, with germination more successful at 21°C than at 25°C and greatest in slightly alkaline (pH 8) germination solution containing KHCO3, CaCl2 and MgSO4 mimicking the mesotrophic humic waters in which the species naturally occurs. In the alkaline solution, 97% of seeds rose to the surface prior to germination. In natural habitats, this effect may facilitate seedlings reaching the warmer and irradiated water surface. As seed germination success appears linked to light availability, water chemistry, and seed position in the water column, careful management and ecological restoration of remnant habitats harbouring this species may need to ensure positive conservation outcomes.
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
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The Southern ground-hornbill (Bucorvus leadbeateri), which is the largest cooperatively breeding bird, is listed as Vulnerable globally and Endangered in South Africa. It occurs from southern Kenya, to the Eastern Cape province in South Africa. Reintroduction protocols used in South Africa can be applied throughout the species range, and to the species congener, the Northern/ Abyssinian ground-hornbill (Bucorvus abyssinicus). A specialized captive rearing center has been built to ensure that the redundant, second-hatched, wild chicks harvested for the reintroduction program have optimal physiological attributes and behavioral skills to survive and reproduce post-reintroduction. Juvenile males identified for reintroduction must go through a minimum of three years in a wild group, called a ‘bush-school’ where wild-experienced group members mentor them in survival skills. They are then paired with a naive female mate to form a new breeding group, and additional helpers are added to the group annually for mentoring until the group successfully begins to breed.
... To verify a preference of vegetative to generative reproduction, we also counted the number of germinating plants of P. praelongus, the determination of which was based on our knowledge of seed germination stages and plantlet growth from laboratory germination tests Prausová, Sikorová, & Šafářová, 2015). ...
... Although the reproduction of P. praelongus was not a focus of our study, we observed that the Nordic populations rarely reproduced with achenes. Although achenes of P. praelongus gathered in Czech localities can germinate aer interruption of their dormancy Prausová, Sikorová, & Šafářová, 2015), seed germination success and subsequent growth of the plantlets in natural sites in Central Europe is expected to be relatively low because of low water transparency, threats by herbivores and competitive organisms (algae, mosses, vascular plants, ducks, and fish), and disturbances (such as floods). However, small plantlets that had germinated from seeds were observed in natural localities in Norway (Prausová, Kozelková, Tomášová, Brodský, Havelka, Pitelková, & Hašler, 2017). ...
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One of the most southern European occurrences of Potamogeton praelongus is in the Czech Republic (CR), with only one native population in the Orlice River floodplain in Eastern Bohemia, the only surviving site from 10 Czech localities known 45 years ago. This species is critically endangered in the CR and needs to be actively protected with a rescue program. The number of P. praelongus sites increases along a latitudinal gradient, from Central to North Europe (CR, Poland, Sweden, and Norway), and correlates with improving conditions (water transparency and nutrient content in water) for this species along this gradient. Although differences in site conditions between Central and North Europe were caused by changes in landscape geomorphology and vegetation during the glacial and postglacial eras, presently, anthropogenic impact is primarily observed. The Czech sites for P. praelongus have distinctly lower water depth and transparency, and conversely, higher conductivity, temperature, and shade levels than the Nordic ones. These extreme conditions in most biotopes of this light-demanding and mesotrophic species in the CR result in lower fitness and different morphological parameters in the Czech populations. These changes lead to decreased competitive ability against filamentous algae and more competitive aquatic plant species and increase the impact of animals. The Nordic nonintensively managed landscape provides numerous large, deep lakes, which are optimal for this aquatic species. In the CR, P. praelongus can currently only survive in rivers and their oxbows, but these are heavily influenced by intensive landscape management and fishing. Comparison of the populations and their site conditions in the CR and other European countries showed that all Czech native and artificially established sites are exposed to eutrophication and its consequences, which are the most important factors affecting the survival of P. praelongus .
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
Chapter
A case study and appraisal of success of wild-to-wild translocations of the endangered Mallee Emu-wren. Translocations for this species were required because large wildfires were reducing the number of extant populations over decades. Ultimately, translocations were deemed "Partially Successful" - Survival rates during transport were high and birds bred and reared young following release. However, a new population failed to establish.
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
... The species is endangered by eutrophication, which results in high phytoplankton and filamentous algae biomass and low summer water transparency. Parts of shoots covered with algae necrotize and die (Prausová et al., 2015). Eutrophication of the Czech localities of LSP resulted in its being replaced by natant broadleaved pondweeds, Nuphar lutea, in small and shallow pools with littoral species and aquatic moss Calliergonella cuspidata. ...
... The growth of LSP is also limited by the influence of animals, especially herbivore fish Ctenopharyngodon idella and Mallard duck (Anas platyrhynchos). Czech populations reproduce only clonally even though germination tests confirmed a germination ability (after interruption of their dormancy) of achenes gathered in Czech localities (Prausová et al., , 2015. The success of seed germination and subsequent growth of its plantlets in natural sites in the CR is unlikely because of low water transparency, threat by herbivores and competitive organisms, and disturbances like floods. ...
Chapter
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The Hermann tortoise (Testudo hermanni, Gmelin, 1789) is exposed to multiple threats in Europe. Populations of both western (T. h. hermanni) and eastern subspecies (T. h. boettgerri) are fading throughout their geographic range. Listed on the Appendix II (A) of the CITES, it is classified as "near threatened" on the IUCN World Red List, but the western subspecies is considered "vulnerable" on the French national red list. The situation of the western subspecies is particularly worrying. Continuous declines since the beginning of the XXth century in Italy, France and Spain resulted in strongly fragmented and reduced populations. In continental France, only one population located in and nearby the Maures Mountains (Var district, South east) persists. Classified as “Endangered” (IUCN regional status) this population is particularly vulnerable due to habitat loss, forest fire, and illegal harvesting. Conservation projects involve sensitization, habitat management and translocation. We tested the efficiency of using rescued individuals to re-enforce the most weakened populations. Following preliminary experiments, we present the results from a second monitoring of successful translocation. Here, we paid attention to the origin of individuals, site selection, and we included different age classes in the program. To minimize possible negative effect of persistent dispersal we used resetting-translocation to the release point: over-dispersing individuals were put back to the initial point of release. Expectedly, individuals prone to over dispersal may surrender and eventually decide to settle into the targeted area. Most (85%) of the released individuals did not settle, showing over dispersal and moving beyond that limit of 1km targeted in this project. Therefore they did not remain within the boundaries of the protected host area. Our previous studies showed that tortoises are more likely to experience mortality during prolonged dispersal, especially when they cross unfavorable habitats or dangerous obstacles. Only two juveniles settled under the 1km limit the first year. Therefore, we put over-dispersing individuals back to the initial release point. A single resetting-translocation was successful for 50% of the over dispersing tortoises; further resetting-translocations (1-2) were successful for 21% more tortoises. Overall, following (1-3) resetting-translocations, only ~25% of the released individuals did not settle in the targeted area. After 15 months, high survival rate (100%) and stable body condition of the individuals suggested that translocation procedures were successful. Importantly, this included supposedly highly vulnerable juveniles. Our results show that individuals adapted well to their novel environment, finding enough trophic resources to maintain their body condition within a normal range (i.e. not different compared to resident host tortoises). Resident individuals did not display any sign of perturbation due to the introduction of exogenous individuals. Resetting-translocation to the release point were essential to promote settlement into the targeted area, and thus likely to enhance survival of the released individuals.
... The species grows in neutral to slightly alkaline waters (Rintanen, 1996;Vöge, 2002;Mäemets et al., 2010;Prausová et al., 2014), mainly in lakes, river floodplains (river oxbows, pools), moderately flowing water, ponds, and reservoirs. It prefers unpolluted, mesotrophic, 0.2-2.0 ...
... Although no seedlings of P. praelongus have been found in Czech natural localities yet, the gathered seeds were able to germinate in several germination tests (Prausová et al., , 2014. Pollination of P. praelongus with pollen of other related species exists in natural conditions. ...
Article
A hybrid of P. praelongus and P. lucens (P.×jutlandicus) was found in an outdoor germination test in 2013–2015, which confirmed existence of spontaneous hybridization of the pondweed species present in the ponds below Plešivec in the Kokořínsko Protected Landscape Area in the Czech Republic. Seedlings of P. ×jutlandicus were different from those of P. praelongus and the speed of their growth was higher. P. ×jutlandicus has not been found in natural sites in the Czech Republic yet. The Czech locality is the third one of this rare hybrid worldwide and the first one with a molecular proof.
... Potamogeton praelongus is known to be sensitive to eutrophication. According to Prausová et al. (2011Prausová et al. ( , 2014 it is critically endangered in the Czech Republic and also in all of Central Europe. Stuckenia filiformis has another record from Lake Eğrigöl, Geyik Mountains of Antalya at 2060 m altitude. ...
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Studying the effect of altitude on species distribution may help us to predict the response of species to future climate changes, which will likely cause upward migration of vegetation zones. In this study, we aimed to analyze distribution and abundance patterns of Potamogetonaceae along an altitudinal gradient and to determine the species characterizing a priori defined five altitudinal groups. We included 294 sampling for 19 species from 141 wetlands across Turkey with an elevation gradient of 2700 m. Analysis of similarities (ANOSIM) found significant differences in species assemblages only between some altitudinal groups. Seven species were found in either high or low altitudes. Stuckenia pectinata had the highest contribution to all groups except one in analysis of similarity percentages. Detrended correspondence analysis revealed a clear altitudinal gradient by placing species under six clusters. Even widespread species occurring in all altitudes showed a tendency of altitudinal preference. The results were inferred from our physicochemical measurements for the species and relevant literature. Exclusively highland species were found in waters with similar physical and chemical properties (i.e. low electrical conductivity, salinity, and ammonium concentrations). However, lowland species were sampled from very diverse aquatic habitats. Among the lowland species Potamogeton acutifolius was found under low values for the above-mentioned physicochemical water parameters but Althenia orientalis showed extremely high values, as well as Potamogeton coloratus and Potamogeton nodosus. Understanding elevational distribution of macrophytes is especially important due to difficulties in their upward migration and availability of suitable aquatic habitats.
... Potamogeton praelongus prefers vegetative to generative reproduction in its whole range [2]. Germination tests were conducted during 2007-2013 to determine how to use the generative reproductive ability of the plant, which is strongly restricted by dormancy [8,15]. A P. praelongus tissue culture was set up in Ostrava (Czech Republic) and 30 clones are maintained there at present. ...
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The aim of the experiment was to determine suitable substrate type and optimal plant size for transfer of plantlets from in vitro to ex vitro under experimental outdoor conditions. Tests focused on the effect of substrate type (muddy and sandy) and starting size of plantlets gained through in vitro seed germination (0–3, 3.1–5,5.1–6, 6.1–10 cm) on plant growth. Three parameters (fresh weight, length, and the number of leaves) were compared to evaluate growth. Basic water parameters in experimental water tanks were regularly measured (pH, temperature, electrical conductivity, shadow intensity) and controlled to reach similar conditions to those in the natural habitat of this species. Overwintering was studied in a cellar with newly defined size categories (≤6, 6.1–8, 8.1–10, 10.1–12, 12.1–15 cm). Both substrate type and starting size of plantlets significantly impacted growth. Plantlets grew better in the muddy substrate while a 100% success rate of rooting was gained with a starting size of 6.1–10 cm in both substrates. The biggest increase in fresh weight was observed with a starting size of 3.1–5 cm and 5.1–6 cm in both substrates. The greatest increase in fresh weight was observed in plants with a starting size of 3.1–5 cm in the muddy substrate (more than 95% increase). The best overwintering results were gained in the 6.1–8 cm size category.
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This publication has been prepared by IUCN (International Union for Conservation of Nature). The designation of geographical entities in this book, and the presentation of the material, do not imply the expression of any opinion whatsoever on the part of the European Commission or IUCN concerning the legal status of any country, territory, or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The views expressed in this publication do not necessarily reflect those of the European Commission or IUCN
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Submersed vegetation is a common feature in about 70% Pyrenean high mountain (>1500 m a.s.l.) lakes. Isoetids and soft-water elodeids are common elements of this underwater flora and can form distinct vegetation units (i.e. patches of vegetation dominated by different species) within complex mosaics of vegetation in shallow waters (<7 m). Since isoetids exert a strong influence on sediment biogeochemistry due to high radial oxygen loss, we examined the small scale characteristics of the lake environment (water and sediment) associated to vegetation patches in order to ascertain potential functional differences among them. To do so, we characterised the species composition and biomass of the main vegetation units from 11 lakes, defined plant communities based on biomass data, and then related each community with sediment properties (redox and dissolved nutrient concentration in the pore water) and water nutrient concentration within plant canopy. We also characterised lake water and sediment in areas without vegetation as a reference. A total of twenty-one vegetation units were identified, ranging from one to five per lake. A cluster analysis on biomass species composition suggested seven different macrophyte communities that were named after the most dominant species: Nitella sp., Potamogeton praelongus, Myriophyllum alterniflorum, Sparganium angustifolium, Isoetes echinospora, Isoetes lacustris and Carex rostrata. Coupling between macrophyte communities and their immediate environment (overlying water and sediment) was manifested mainly as variation in sediment redox conditions and the dominant form of inorganic nitrogen in pore-water. These effects depended on the specific composition of the community, and on the allocation between above-and belowground biomass, and could be predicted with a model relating the average and standard deviation of sediment redox potential from 0 down to -20 cm, across macrophyte communities. Differences in pore-water total dissolved phosphorus were related to the trophic state of the lakes. There was no correlation between sediment and water column dissolved nutrients. However, nitrate concentrations tended to be lower in the water overlaying isoetid communities, in apparent contradiction to the patterns of dissolved nitrates in the pore-water. These tendencies were robust even when comparing the water overlaying communities within the same lake, thus pointing towards a potential effect of isoetids in reducing dissolved nitrogen in the lakes.
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Schulz, Sister M. Richardis, O.P., and Richard M. Klein. (N. Y. Bot. Gard., N. Y., N. Y.) Effects of visible and ultraviolet radiation on the germination of Phacelia tanacetifolia. Amer. Jour. Bot. 50(5): 430–434. Illus. 1963.—Germination of Phacelia tanacetifolia was suppressed by exposure to white light increasing with intensity and length of illumination. The light effect decayed during 24 hr of darkness. Seeds were most sensitive to the suppressive effects of light 13–17 hr after the beginning of imbibition. Light suppression was caused by a photocatalytic reaction. Wavelengths causing the suppression lie in the far-red, red, blue, near-ultraviolet and far-ultraviolet regions of the spectrum. At equal energies, blue light was less effective than far-red, red or ultraviolet radiation. There was no evidence for the existence of the phytochrome system. Simultaneous irradiation with red and blue light or simultaneous irradiation with red and far-red induced a synergistic repression of germination. The presentation of different wavelengths in various sequential patterns markedly altered the germination response. An interaction between elevated temperatures and visible radiation affecting germination response was also noted.
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The storage and germination environments were evaluated to determine the cause of low total germination percentages and highly irregular germination of Coreopsis lanceolata L. seed. Highest total germination and most rapid and uniform germination of seed occurred at constant 15C, other constant temperatures and all alternating temperature regimes caused lower total germination or delayed it. Seeds tolerated -20C during storage, but total germination was reduced below -5C. Recently harvested seeds had 44% total germination, but 54% to 81% germination was achieved after 6 hours of soaking seeds in 1000 ppm GA 3 , 1000 ppm ethephon, or 25 ppm kinetin alone or in combination. Growth regulators reduced the number of days to 50% of final germination (T 50 ), and the span in days between 10% and 90% of germination (T 90 - T 10 ). Storing fresh seeds without chemical treatment for > 6 months at 5C and 10% to 20% relative humidity (RH), or 15C at 20% to 35% RH, increased total germination to 75% and 80%, respectively. Ten days were required to achieve T 50 after 5 to 6 months of storage at 5C and 10% to 20% RH or 15C and 10% to 40% RH, with longer periods to T 50 at other storage durations and RH levels. The germination spans (T 90 - T 10 ) were lengthened the higher the seed storage temperatures between 5 to 25C, with longer spans as seed storage durations and relative humidities increased. Total germination was similar after storing seeds at 5 or 15C and 10% to 30% RH and after soaking recently harvested seeds in GA 3 + ethephon, but the days to T 50 and T 90 - T 10 were shorter after growth regulator treatment. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); gibberellic acid (GA 3 ); 6-furfurylaminopurine (kinetin).
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The knowledge of the flora of the Czech Republic has substantially improved since the second version of the national Red List was published, mainly due to large-scale field recording during the last decade and the resulting large national databases. In this paper, an updated Red List is presented and compared with the previous editions of 1979 and 2000. The complete updated Red List consists of 1720 taxa (listed in Electronic Appendix 1), accounting for more then a half (59.2%) of the native flora of the Czech Republic. Of the Red-Listed taxa, 156 (9.1% of the total number on the list) are in the A categories, which include taxa that have vanished from the flora or are not known to occur at present, 471 (27.4%) are classified as critically threatened, 357 (20.8%) as threatened and 356 (20.7%) as endangered. From 1979to 2000 to2012, there has been an increase in the total number of taxa included in the Red List (from 1190to 1627 to 1720) and in most categories, mainly for the following reasons: (i) The continuing human pressure on many natural and semi-natural habitats is reflected in the increased vulnerability or level of threat to many vascular plants; some vulnerable species therefore became endangered, those endangered critically threatened, while species until recently not classified may be included in the Red List as vulnerable or even endangered. (ii) Some increase in the number of species in particular categories can be attributed to the improved knowledge of taxonomically difficult groups for which previously only incomplete species lists were available. In addition, some native species were recently discovered as new to the country's flora or described as new to science, and the status of their populations made Red-Listing necessary. (iii) Also improvements in our knowledge of the flora made the expertjudgment more precise and some species were included in the list because their long-lasting vulnerability was recognized. In contrast, 23 taxa considered extinct or missing were rediscovered. This is almost one third of the number of extinct or missing taxa in the first version of the Red List published in 1979.
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In the laboratory, 14 macrophyte species grown in the absence of herbivores had growth rates of 1-10%/d. When grown with 4 densities of herbivorous snails, species that grew fastest in the absence of herbivores were, in general, most negatively influenced by grazing. Snails typically preferred the plant species that grew fastest in the absence of herbivores. Snail densities were manipulated in the small mesotrophic Christmas Lake. Where high snail densities were maintained, macrophyte species richness decreased; the plants remaining were the species least preferred in choice tests. For the leaves examined of one macrophyte, 6-113% of one total leaf area was lost to herbivores.-from Author
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Germination of Phacelia tanacetifolia was suppressed by exposure to white light increasing with intensity and length of illumination. The light effect decayed during 24 hr of darkness. Seeds were most sensitive to the suppressive effects of light 13-- 17 hr after the beginning of imbibr-tion. Light suppression was caused by a photocatalytic reaction. Wavelengths causing the suppression lie in the far-red, red, blue, near-ultraviolet, and far- ultraviolet regions of the spectrum. At equal energies, blue light was less effective than far-red, red, or ultraviolet radiation. There was no evidence for the existence of the phytochrome system. Simultaneous irradiation with red and blue light or simultaneous irradiation with red and far-red induced a synergistic repression of germination. The presentation of different wavelengths in various sequential patterns markedly altered the germination response. An interaction between elevated temperatures and visible radiation affecting germination response was also noted. (auth)
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Factorial laboratory germination experiments were carried out on fruits from 10 British species of Potamogeton (Potamogetonaceae). Fruits had all been placed in a dry-room maintained at 15% RH and 15°C for 3–6 months from the time of collection.Maximum levels of germination ranged from 13% (P. polygonifolius) to 90% (P. berchtoldii). Whilst for some species, there was some germination across all the conditions tested, for others germination was significantly increased under specific conditions. The single most important factor for promoting germination was cold stratification prior to placing at the germination temperature. Logistic regression analysis indicated that there was a positive effect of applying a cold stratification treatment in P. filiformis, P. gramineus, and P. natans. Scarification (removal of some of the fruit) also resulted in increases in the number of seeds that germinated for all species.It is suggested that the initial conditions which should be tried for germinating seeds from temperate Potamogeton species are 15–20°C with a 12h photoperiod, anaerobic conditions, following a cold stratification treatment. If high levels of germination are not observed, the fruits should be scarified to remove the mechanical restriction of the fruit coat.
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The germination of seeds of seven plant species occurring in a dune grassland vegetation of the Netherlands, was studied at four levels of UV-B radiation simulating unto 45% stratospheric ozone reduction during April. With the exception of seeds of Senecio jacobaea, germination of the dune grassland species was not affected by enhanced UV-B irradiance. Although a clear UV-B fluence-response relationship was not observed, the germination rate of S. jacobaea seeds and maximal germination percentage were reduced at enhanced UV-B. Germination rate in the dark was higher than germination in the light for Oenothera biennis, Plantago lanceolata, Rumex obtusifolius and S. jacobaea. Total dry biomass accumulation of seedlings was not affected by increased UV-B radiation in any of the species tested. Clear-cut differences in UV-absorbance of methanolic extracts were observed between species. Enhanced UV-B irradiance stimulated UV-absorbance of seedling extracts of Holcus lanatus and Verbascum thapsus. A clear UV-B fluence-response relationship was observed for both species. The results indicate that germination of the studied plant species probably will not be adversely affected by the expected stratospheric ozone reduction in The Netherlands.
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A study is presented of germination inPotamogeton angustifolius, P. acutifolius, P. obtusifolius, P. crispus, P. lucens, P. natans, P. pectinatus, P. pusillus andP. trichoides, and the possibility of overcoming dormancy in these species under laboratory conditions. Three of the species, viz.Potamogeton pectinatus, P. pusillus andP. trichoides have been examined in greater detail. Impermeability of the fruit coat appears to be the main reason for the dormancy of these species. The lowest percentage of the impermeable achenes has been recorded inPotamogeton crispus.
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Ecological Studies on Waterplants of 14 Sites Around Kangerlussuaq, Southern West Greenland, with Special Regard to Potamogeton Assessment of genetic variation and clonality in these agrass Posidonia australis using RAPD and allozyme analysis
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Ecological Studies on Waterplants of 14 Sites Around Kangerlussuaq, Southern West Greenland, with Special Regard to Potamogeton
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Vöge, M., 2002. Ecological Studies on Waterplants of 14 Sites Around Kangerlussuaq, Southern West Greenland, with Special Regard to Potamogeton. Hamburg, URL: http://www.solo-tauchen.de/PDF/www04.pdf
Die Entwicklung von Potamogeton praelongus im Grossensee bei Hamburg
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