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The diversity and abundance of insect pollinators are declining. This decline reduces the potential ecosystem services of pollination for wild and cultivated plants. Specific agri-environment schemes (AES) are subsidised to support and conserve biodiversity in farmlands. In Belgium, the pollinator flower-strips AES, strips of flower-rich hay meadows, has been promoted as a potential scheme to increase pollinator abundance and diversity, even if their effectiveness has not been locally evaluated. The main objective of this research is to assess the capacity of pollinator-strip AES to provide flower-resources to diverse pollinators. During 2 years, we monthly measured the availability of flower resources (pollen and nectar) produced on four flower-strips surrounded by intensive farming in Belgium. We counted and identified insects that visited these flowers, and we constructed the plant–insect interactions networks. The pollinator-strip AES presented a mix of both sown and spontaneous plant species. The ten sown plant species were all present, even after 8 years of strip settings. Three of them, Centaurea jacea, Lotus corniculatus, and Daucus carota were mainly visited for nectar collection, and a spontaneous non-sown species, Trifolium repens, had a key role in providing high-quality pollen to insects. Most of the observed flower-visiting insects belonged to common species of Hymenoptera and Diptera. All are considered highly efficient pollinators. The Belgian pollinator flower-strips are effective AES that provide flower resources to pollinators, mainly during summer and support pollination services. Nevertheless, spring and autumn flower resources remain poor and could reduce the strips’ effectiveness for supporting long-term insect diversity.

Summary1. Pollinator decline causes great concern because reduced pollinator availability may negativelyaffect plants’ seed production and in turn influence seedling recruitment and densities of plant popu-lations.2. We used a novel experimental approach that simulates pollinator decline to assess the effects of a4-year reduction in pollinator availability on reproduction and recruitment in two common Europeanherbs, Centaurea jacea and Leucanthemum vulgare.3. The experiment strongly reduced visitation rates (by 59%) and seed set (by 23%) in Leucanthe-mum, but this did not cause reduced seedling recruitment, suggesting that other factors, such aswater availability or the existence of a seed bank, are important for recruitment in this population ofLeucanthemum.4. The experiment also significantly reduced visitation rates to Centaurea (by 33%), but did notaffect seed set or seedling recruitment. In this species, however, seed set increased with visitationrates and local recruitment increased with seed production, indicating that a consistent pollinatordecline may negatively affect Centaurea population densities.5. Synthesis. Our experiment reduced pollinator availability without artificially affecting qualitycomponents of the pollination process. Therefore, this approach may represent a realistic simulationof a pollinator decline. To our knowledge, this is the first study that uses an experimental reductionin pollinator visitation to assess its effects on population recruitment in plants. This study shows thata large pollinator decline may affect population densities, but only in populations where seedlingrecruitment is limited by seed production. Our results also highlight the importance of going beyondvisitation rates and seed production to study the impact of pollinator decline on plant populations.Key-words: Centaurea jacea, Leucanthemum vulgare, pollinator loss, reproductive ecology, seedset, seed weight, seedling density, visitation rateIntroduction

Sown wildflower strips are increasingly being established in Europe for enhancing arthropod conservation and the provision of ecosystem services, including biotic pollination and natural pest control. Here we use floral traits to identify different plant functional effect groups. Floral resources were provided in four experimental levels characterised by a cumulatively increasing flower trait diversity and vegetation stand complexity. The first level consisted of a bare control strip, whilst in each subsequent level three wildflower species with different functional traits were added (Level 0: control; Level 1: three Apiaceae species; Level 2: three Apiaceae and three Fabaceae species; Level 3: three Apiaceae, three Fabaceae species, and Centaurea jacea (Asteraceae), Fagopyrum esculentum (Polygonaceae), Sinapis alba (Brassicaceae)). Plots with sown wildflower strip mixtures were located adjacent to experimental plots of organically-managed tomato crop, which is attacked by multiple pests and partially relies on bees for fruit production, and hence dependent on the provision of pollination and pest control services. Results obtained here show that the inclusion of functionally diverse wildflower species was associated with an augmented availability of floral resources across time, and this increased the abundance of bees and anthocorids throughout the crop season. Several natural enemy groups, such as parasitoids, coccinelids and ground-dwelling predators, were not significantly enhanced by the inclusion of additional flower traits within the strips but the presence of flower resources was important to enhance their conservation in an arable cropping system.

According to traditional theory, success in competition between plant species generally involves a ‘size-advantage’. We predicted therefore that plants with larger body size should impose greater limits on the number of species — especially relatively small ones — that can reside within their immediate neighbourhoods. Species composition was compared within local neighbourhoods surrounding target plants of different sizes belonging to one of the largest herbaceous species found within old-field vegetation in eastern Ontario Canada — Centaurea jacea. Resident species density was generally greater within immediate ‘inner’ target neighbourhoods than within adjacent circular ‘outer’ neighbourhoods, and mean body size of resident neighbour species was unrelated to increases in target plant size. As target plant size increased, the proportion of resident neighbour species that were reproductive increased. Relatively big plants of C. jacea do not limit the number or the proportion of reproductive species that can coexist within their immediate neighbourhoods, nor do they cause local exclusion of relatively small species from these neighbourhoods. These results fail to support the ‘size-advantage’ hypothesis and are more consistent with the ‘reproductive economy advantage’ hypothesis: success under intense competition is promoted by capacity to recruit offspring that — despite severe suppression — are able to reach their minimum body size needed for reproduction, and hence produce grand-offspring for the next generation. The latter is facilitated by a relatively small minimum reproductive threshold size, which is generally negatively correlated with a relatively large maximum potential body size.

The non polar extract of Centaurea pannonica (Heuff.) Simonk., growing wild in Serbia, was studied and twenty-five compounds including 14 sesquiterpene lactones, 7 flavonoids, 3 lignans and 1 phenylpropanoid glycoside were isolated. All compounds were isolated for the first time from this species. Among them, one germacranolide 2α-hydroxy, 8-dehydroxy 15-O-methacrylate salonitenolide (1) and two guaianolides 2α,8α-dihydroxy-dehydrocostus lactone (2) and pannonin (3) are new natural compounds. The structures of the compounds were established on the basis of spectroscopic analyses (UV, IR, HREIMS and 1D & 2D NMR). The chemical profile of C. pannonica, which belongs to the “Centaurea jacea” group, was compared to previously studied taxa of the same group and used to assess the phylogenetic relationships in the group.

Janzen–Connell effects are negative effects on the survival of a plant's progeny at high conspecific densities or close to its conspecifics. Although the role of Janzen–Connell effects on the maintenance of plant diversity was frequently studied, only few studies targeted Janzen–Connell effects via postdispersal seed predation in temperate grassland systems. We examined effects of conspecific density (abundance of conspecific adult plants) on postdispersal seed predation by invertebrates of three grassland species (Centaurea jacea, Geranium pratense, and Knautia arvensis) in experimental plant communities. Additionally, we examined the impact of plant species richness and different seed predator communities on total and relative seed predation (= seed predation of one plant species relative to others). We offered seeds in an exclusion experiment, where treatments allowed access for (1) arthropods and slugs, (2) arthropods only, (3) small arthropods only, and (4) slugs only. Treatments were placed in plots covering a gradient of abundance of conspecific adults at different levels of plant species richness (1, 2, 3, 4, 8 species). Two of the plant species (C. jacea and K. arvensis) experienced higher rates of seed predation and relative predation with increasing abundance of conspecific adults. For C. jacea, this effect was mitigated with increasing plant species richness. Differences in seed predator communities shifted seed predation between the plant species and changed the magnitude of seed predation of one plant species relative to the others. We exemplify density‐dependent increase in seed predation via invertebrates in grassland communities shaping both the total magnitude of species‐specific seed predation and seed predation of one species relative to others. Further differences in seed predator groups shift the magnitude of seed predation between different plant species. This highlights the importance of invertebrate seed predation to structure grasslands via density‐dependent effects and differing preferences of consumer groups.

Climate change enables range expansions of plants, animals and microbes to higher altitudes and latitudes. Plants may benefit from range expansion when they escape from natural enemies. However, range expansion becomes a disadvantage when plants become disconnected from organisms that control enemies in the new range. Here, we examined nematode control in the root zone of range-expanding plant species and congeneric natives. In a greenhouse, we determined bottom-up (by the plants) and top-down (by natural enemies of the nematodes) control of two root-feeding nematode species (Helicotylenchus pseudorobustus and Meloidogyne hapla) in the rhizospheres of two range-expanding plant species, Centaurea stoebe and Geranium pyrenaicum, and two congeneric natives, Centaurea jacea and Geranium molle. Pots with plants growing in sterilized soil were inoculated with either a microbial soil community from the newly colonized natural habitat, a mixture of native microbial nematode antagonists, or a combination of these two communities. We tested the hypotheses that bottom-up control of root-feeding nematodes would be strongest in the root zone of range expanders and that top-down control would be strongest in the root zone of native plant species. We observed profound intra- and interspecific differences in bottom-up and top-down control among all four plant species. Bottom-up control by the range-expanding plant species was either strong or weak. Top-down control by microbes was strongest in native Centaurea. The addition of a mixture of both microbial communities reduced control of M. hapla in the root zones of the native plant species, and enhanced its control in the root zones of range-expanding plant species. We conclude that there was species-specific bottom-up and top-down control of root-feeding nematodes among the four plant species tested. Range-expanding plant species influenced their microbial rhizosphere community differently compared to native plant species, but top-down control in the root zone of natives was not systematically superior to that of range-shifting plant species.

The article presents the results of research (2005-2011 years) of Centaurea jacea L. aсlonist large lifecycle. There are described in detail the age and stage of plant features. Widely covered the stages of shoot system formation.

The mobility and phytoavailability of arsenic in an area affected by the abandoned exploitation of an arsenical tungsten–tin deposit was studied to establish the current and eventual environmental risks and to propose possible remediation practices. Soil and plant samples were collected at different distances from the polluting sources and analyzed for their As content and distribution. Critical soil total concentrations of As were found, with values in the range 175–2300 mg kg − 1 . The readily labile As contents represent Agrostis castellana (Boiss. & Reut.), Centaurea jacea L., Eryngium campestre L. and Scirpus holoschoenus L.. Such plants show important root bioaccumulation factor values in relation to the labile As contents (up to 197, 58, 201 and 88, respectively) and low translocation factor values (down to 0.170, 0.032, 0.173 and 0.036, respectively). Additionally to promote the revegetation with these plants, the species Rumex acetosella L. should be eliminated as this behaves as an index plant, reaching above-ground As concentrations up to 218 mg kg − 1 .

We studied the relative importance of the aboveground and belowground environment for survival and growth of emerged seedlings of Centaurea jacea to better understand the general difficulty of establishing late-successional species at restoration sites on ex-arable land. Potted seedlings growing on soil from six late-successional grasslands and from six ex-arable (restoration) sites were reciprocally exchanged, and survival and relative growth rate of the seedlings monitored. In addition, we assessed aboveground herbivory and colonization of roots by arbuscular myccorhizal fungi of all plants, as well as nutrient availability, and microbial biomass and community composition using PLFA techniques in all twelve soils. Seedling survival was higher in restoration habitat and soil than in grassland habitat and soil, but growth did not differ between the aboveground and belowground environment types. Shoot growth rate was initially correlated with soil nutrient content, and later in the experiment with mycorrhizal colonization levels. Our results indicate that arbuscular mycorhizal fungi may be important for the successful establishment of C. jacea and that abiotic soil factors, like K availability and N:P ratio, can promote mycorrhizal colonization. Hence, the belowground environment should be considered when selecting sites for restoring species-rich grasslands.

There is no report on the chemical composition of alder buckthorn (Rhamnus frangula L.) honey and therefore volatile organic compounds (VOCs) were investigated for the first time as well as their composition after short-term heating. The electrical conductivity of the samples was 0.90 - 0.98 mScm-1 (specificity of alder buckthorn honey), and pH values were 4.00 - 4.33. The melissopalynological analysis revealed R. frangula L. as dominant plant species (52-93%) in all samples. Accompanying minor plant species were also determined (Castanea sativa L., Centaurea jacea L., Lotus corniculatus L., Prunus spp., Salix spp., Apiaceae, Asteraceae, Acer spp. and Cornus sanguinea L.). The VOCs from R. frangula L. honey were isolated by headspace solid-phase microextraction (HS-SPME) and ultrasonic solvent extraction (USE) and analysed by GC-FID and GC-MS. To investigate the influence of short-term heating, selected sample was heated 3h at 100 oC with and without H2O addition. The most representative chemical profile of R. frangula L. honey is obtained by HS-SPME containing benzaldehyde, hotrienol and 4-ketoisophorone. USE contributed to the honey characterization, mainly by vomifoliol identification. The majority of compounds found in USE were higher aliphatic alcohols. The influence of short-term heating to R. frangula L. honey is strongly dependent on H2O addition. Namely, more artefacts (furan derivatives, particularly 5-hydroxymethylfurfural) were formed during heating of the honey dissolved in H2O in comparison with direct honey heating.

We studied the variation in the responses of brown knapweed ( Centaurea jacea ) ecotypes from Finland and Switzerland to elevated O 3 and CO 2 and, the possible role of CO 2 as a factor modifying O 3 sensitivity. Individuals of four C. jacea ecotypes were exposed to elevated O 3 (40 ppb) and CO 2 (450 ppm) alone or in combination in open-top chambers (OTC) in the summer 2003. Open-field plots served as controls for the chamber effect. Ozone effects were mainly manifested as visible injuries: O 3 -specific light brown flecks and non-specific purple pigmentation. The proportion of O 3 -specific visible injuries was highest in the Swiss plants, where they correlated positively with early flowering, high dry matter production and high stem dry weight. CO 2 ameliorated the severity of O 3 -specific visible injuries only in the most O 3 -sensitive ecotype, but diminished the differences between the different ecotypes. Ozone exposure also accelerated plant senescence, which was seen as enhanced development of purple pigmentation. The lack of growth responses may be explained by the low exposure concentrations. The intraspecific differences in O 3 sensitivity may limit the use of C. jacea as a bioindicator for intact vegetation.

Studies in plant demography are primarily done at the level of ramets and typically collect ramet-related parameters such as ramet size, type and history. This approach ignores possible effects of factors associated with higher levels, such as genet or tussock. This is particularly important in perennial resprouting herbs with persistent root that consists of many ramets as interaction between ramets, both by competition and by resource sharing, are likely to be intense in these plants. This study investigates effects of tussock-level parameters (age, size and ramet position within tussock and ramet density) on performance of individual ramets in two tussock-forming resprouting herbs ( Tanacetum vulgare and Centaurea jacea ). The results show that position of a ramet within tussock did not affect ramet growth, but had significant effects on flowering and survival in both species. The direction of the effect differed between the two species; marginal ramets were more successful in T. vulgare , while central ramets were more successful in C. jacea . In addition, tussock age had a significant effect on ramet flowering and survival in T. vulgare . Both these effects are likely to be due to the more competitive life form of T. vulgare , which is restricted to temporary habitats with intense competition. C. jacea is a species of mown or grazed grasslands with lower productivity, which are more stable and where competition is weaker. The effects of the number of neighboring ramets and of the tussock size were significant, but often locality-specific. The results indicate that although many important effects of tussock-related parameters exist, their direction and magnitude differ between species or even populations and are thus not easily predictable. Neglecting these effects, however, is likely to make the demographic models weaker.

1 Many plant species are currently restricted to small and isolated populations as a result of habitat destruction and fragmentation. Lack of sufficient data often leads to spatial variation being substituted for temporal variation in models to evaluate management options, but variation in population growth rate () between sites or over years may be caused by variation in different life history components. 2 We studied the demography of three coexisting and related perennial herbs (the longlived perennial Succisa pratensis, the shorter-lived Hypochaeris radicata and the longlived, but more clonal Centaurea jacea ) in the same plots over 4 years (1999?2003). 3 Life table response experiment analysis revealed that temporal and spatial variation in the life history components of S. pratensis and H. radicata were qualitatively different: variation in fecundity contributed most to variation in between sites, but variation in growth contributed most to variation between years. 4 In years with a below average, most life history components of S. pratensis and H. radicata had lower transition probabilities, whereas the reasons for low population growth differed between the three poor sites. All major life history components of S. pratensis had lower probabilities in the most productive of these sites, but in the other two, negative contributions from some components (fecundity or growth) were partly compensated for by positive contributions from others (growth or stasis). 5 Centaurea jacea showed a different pattern: in poor years, negative contributions from some life history components were buffered by positive contributions from other components; however, this buffering did not occur in poor sites. 6 Our analysis shows that the population dynamics of perennial plants may respond differently to temporal and spatial variation in environmental conditions. Moreover, co-occurring species with similar life histories responded differently to the same spatiotemporal variation. We conclude that temporal and spatial dynamics cannot readily be interchanged in population viability analyses and management studies, as such substitution may lead to incorrect projections of a species? population dynamics in time. Key-words : buffering of variation, demography, life history components, population growth rate, variation decomposition.

The effect of the seed abscission process on the dispersal distance of seeds has never been studied explicitly and is often ignored in studies that aim to estimate the seed shadows of species. To examine the importance of the abscission process for the seed shadow we used a seed trajectory model that keeps track of the release threshold dynamics of the individual seeds on mother plant. We defined the release threshold as the critical wind speed that induces a mechanical force that is just large enough to release a seed from its mother plant. The model used real wind speed sequences and seed appearance over time on the mother plant. Several calculations were performed to investigate the effect of release thresholds dynamics on seed shadow of two herbaceous species with contrasting terminal velocity values ( V t ): Centaurea jacea ( V t = 4.1 m s −1 ) and Hypochaeris radicata ( V t = 0.49 m s −1 ). Release thresholds were responsible for a two-fold increase of median dispersal distances in both species. Tails of the seed shadows, the fraction of seeds that travel furthest, were even more sensitive and increased with a factor 4.5 for Centaurea and 7.0 for Hypochaeris . Our work indicates that the abscission process appears to be very important and suggests that dispersal distance of plants is currently severely underestimated, which, in turn, has major consequences for our current understanding of the distribution, metapopulation dynamics and survival of plant species.

Brown knapweed (Centaurea jacea L.) has been suggested as a potential bioindicator for tropospheric ozone (O3), but little is known about the intra-specific variation in O3 sensitivity in this wild species. The aim of this study was to quantify the differences in O3 sensitivity among and within five populations, and to relate the differences to morphological, phenological, and genetic characteristics. These parameters were periodically recorded in two consecutive experiments on a total of 357 plants from five different European countries (Norway, Hungary, Switzerland, Italy, Slovenia). They were grown from seed in natural soil under ambient conditions at a site with seasonally elevated O3 concentrations (Cadenazzo, southern Switzerland). The populations differed significantly both in frequency and extent of O3 injury, as well as in phenological development. The observed degree of O3 injury was highest in the Slovenian and the Swiss populations, while only few Hungarian and Norwegian plants showed slight symptoms of injury. Plants were generally most sensitive to O3 when reaching the reproductive stage, and insensitive at the rosette stage. Amplified fragment length polymorphism analysis (AFLP) demonstrated genetic distinctiveness of the five C. jacea populations. All individuals of four of the five populations were correctly assigned to the respective populations based on principal component analysis. Cluster analysis quite accurately reflected the geographic origin of each population. Overall, the analysis revealed a high degree of intra-specific variability in O3 sensitivity in C. jacea, and underlined the important influence of the climate-dependent population-specific plant development on O3 sensitivity. These observations may constrain the development of a standardized biomonitoring system.

Flexible life history responses to flower and rosette bud removal in three perennial herbs Nienke Hartemink, Eelke Jongejans and Hans de Kroon, In a garden experiment we investigated the response to continuous removal of either flower buds or rosette buds in three perennial grassland species (Hypochaeris radicata, Succisa pratensis and Centaurea jacea), which differ in longevity and flowering type. We distinguished two possible responses: compensation for lost buds by making more buds of the same type, and switching towards development of other life history functions. Both responses were demonstrated in our experiment, but bud removal had significantly different effects in each of the three species. The degree of compensation and the expression of trade-offs between life history functions differed markedly between species and seem related to longevity and developmental constraints. With respect to switching, our results suggest costs of reproduction and a trade-off between life history functions, at least for Hypochaeris and Succisa. For these species weight of new rosettes increased when resource allocation to flowering was inhibited. In Hypochaeris, we see that both compensation for lost flower buds and switching from lost rosette buds increased production of flower buds, underscoring the pivotal role of sexual reproduction in this short-lived species. The most prominent response seen in Centaurea is compensation for lost rosette buds, indicating that this long-lived species with monocarpic rosettes relies on rosette formation. Although Succisa does respond to bud removal, time is an important constraint in this species with long-lived rosettes and preformed flowering stalks. Trade-offs in Succisa seem to operate at a larger time scale, requiring long-lasting experiments to reveal them. We conclude that the response of these species to inflicted damage is likely to be linked to their longevity and developmental constraints.

The structure of invertebrate communities is impacted by landscape variables. Here we present a study on the influence of the surrounding matrix on pollinating flower visitors of the knapweed Centaurea jaceain a small-scale agricultural landscape (Central Hesse, Germany). The study was carried out in late summer 1998 by monitoring visits of 24 insect taxa at 15 C. jacea patches. The following matrix types were studied: (i) arable land only, (ii) arable land close to grassland (

The Centaurea jacea aggregate is a polymorphic polyploid complex whose taxonomic treatment is still controversial. A numerical taxonomic approach was applied to 394 individuals of known ploidy level, from 19 populations, based on the main diagnostic characters proposed in earlier revisions. Populations from xeric grasslands were not considered. Principal Component Analysis shows that variation within the complex is continuous. UPGMA Cluster Analysis based on population means supports the recognition of three groups of populations. However, the limits between these groups are blurred to a considerable extent due to extensive within-population polymorphism. It is argued that the Belgian populations of Centaurea jacea occurring in mesic grasslands should be treated as a single species, with three subspecies. The two extremes of the morphological gradient can be referred to as C. jacea subsp. jacea and C. jacea subsp. nigra, with C. jacea subsp. pratensis occupying an intermediate position. Most populations from Belgium are tetraploid, a diploid chromosome number being found only in populations of C. jacea subsp. nigra from the Ardennes massif. On average, diploids grow at higher altitude and on more acidic soils than tetraploids. Finally, a key to the three subspecies is provided., SCOPUS: ar.j, FLWIN, info:eu-repo/semantics/published

Ethnopharmacological relevance Palynological studies of cultural layers of cave sediments have been used in order to better understand traditional practices. The Upper Palaeolithic in Georgia (36,000−11,000 cal. BP) provides a rich source of such material. However, up to day from such sediments the identification of medicinal plants has hardly been achieved. Large quantities of pollen most notably from entomophilous taxa in fossil spectra can serve as a tool to identify traditionally important species. As these plants are used in modern popular medicine on the territory of Georgia (like Achillea millefolium L., Artemisia annua L., Artemisia absinthium L., Centaurea jacea L., Urtica dioica L.) can be served as an indirect evidence for their medicinal relevance from the Palaeolithic Period up to days. Their modern uses may point that the main diseases during the Upper Palaeolithic were the same as today. Materials and methods The Upper Palaeolithic sediments were studied palynologically come from four caves: Dzudzuana, Satsurblia, Kotias Klde and Bondi. Modern sediments were investigated from 6 caves. Fossil and modern samples were taken according to the standard procedure in palynology. The laboratory treatment was carried out as follows: first, 50 g of the sample was boiled in 10% KOH. At the second stage, centrifuging of the material in cadmium liquid was performed. At the final stage, acetolysis treatment was used. Results Pollen of A. absinthium L. (Asteraceae), A. annua L. (Asteraceae), A. millefolium L. (Asteraceae), C. jacea L. (Asteraceae), and U. dioica L. (Urticaceae) are identified to species level. This species are not edible and are popular in present-day folk medicine. In the Upper Palaeolithic layers, significant amounts of studies species pollen were recorded in the cave, likely due to their flowering branches being brought in by humans for use. Detailed consideration of the pharmacological characteristics of the examined species showed that almost all of them have anti-inflammatory, antibacterial, antimicrobial and antipyretic activity. Conclusion The fossil pollen complex of medicinal herbs, dominated by A. millefolium and Artemisia ( A. annua and A. absinthium ), suggests that the ancient population living in the studied caves could have been prone to malaria, rheumatism and gastrointestinal diseases. In the Upper Palaeolithic, the population inhabiting cave sites might have suffered from gout and callouses.

I examined two aspects of how recruitment is influenced by species richness in a seminatural grassland: effects of species richness among colonisers in a seed mixture, and effects of species richness, ramet density, grass and moss cover in the colonised vegetation. The results suggest that recruitment is higher in more species-rich seed mixtures (for three of the four target species: Anthyllis vulneraria, Centaurea jacea, Filipendula vulgaris and Primula veris). Average recruitment of the target species was negatively related to ramet density in the colonised vegetation, but not affected by grass or moss cover. The results imply that mechanisms other than interspecific competition among species are important in structuring the community during the recruitment phase. The negative effects of ramet density and the positive effects of species richness may be a result of strong intra-specific competition, or species-independent competition in combination with diversity effects enhancing microsite variability.

Summary 1 In order to test the hypothesis that the sensitivity of field populations of the rare perennial Arnica montana to slug attack is due to its high palatability, we compared Arnica leaves and seedlings with 20 other plant species in greenhouse food choice experiments. 2 When slugs were given a choice of mature plant leaf discs, Arnica montana was one of the food plants most preferred by all three slug species tested. Arion lusitanicus, Arionsubfuscus and Deroceras agreste differed only slightly in their preference for particular plant species. Greater differences in acceptability were observed when parameters other than area consumed were evaluated. Arnica seedlings displayed similarly high susceptibility to slug grazing. 3 Morphological factors influence mollusc feeding behaviour, with epidermal cell wall thickness and hairiness related to acceptability. Removing the hairs by shaving the leaves increased the acceptability of one species, Centaurea jacea. 4 Leaves of undamaged Arnica montana plants were preferred to leaves of plants that had been predamaged by partial leaf removal, suggesting that there is an inducible component of chemical defence. 5 We discuss our results in comparison with other food choice experiments and attempt to extrapolate them to mollusc/plant interactions under field conditions.

Effects of elevated CO2 on flowering phenology and nectar production were investigated in Trifolium pratense, Lotus corniculatus, Scabiosa columbaria, Centaurea jacea and Betonica officinalis, which are all important nectar plants for butterflies. In glasshouse experiments, juvenile plants were exposed to ambient (350 μl l−1) and elevated (660 μl l−1) CO2 concentrations for 60–80 days. Elevated CO2 significantly enhanced the development of flower buds in C. jacea. B. officinalis flowered earlier and L. corniculatus produced more flowers under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar per flower was not affected by elevated CO2 in the tested legumes (T. pratense and L. corniculatus), but was significantly reduced (!) in the other forbs. Elevated CO2 did not significantly affect nectar sugar concentration and composition. However, S. columbaria and C. jacea produced significantly less total sugar under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species, whereas the total of amino acids produced per flower was reduced in all non-legumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as most butterflies which have no alternative food resources to nectar. Changes in nectar production due to elevated CO2 could also have generally detrimental effects on the interactions of flowers and their pollinators.

The influence of sown herb strips on larval stages of aphidophagous syrphids was studied in different strips and adjacent winter wheat fields near Berne (Switzerland) from 1993 to 1995. The aim of this study was to learn whether these sown herb strips offer a supply of aphids sufficient enough to sustain the first generation of syrphids in spring or a further generation after crop harvest. Aphid infestation of the strips occurred at about the same time as in winter wheat, between the end of May and the beginning of August. A first syrphid generation in spring can therefore not develop on weeds in strips. Furthermore, after harvest no further generations will appear in strips. The highest numbers of syrphid pre-imaginal stages in 1993 and 1994 were found on spontaneously growing weeds (Rumex obtusifolius, Cirsium arvense and C. vulgare). Among the sown species, Centaurea jacea and Pastinaca sativa showed the highest syrphid larvae densities. The densities in herb strips (max. 0.6 larvae/m 2 ) were manyfold lower than in wheat (10 pupae/m 2 ). In herb strips the same syrphid species as in winter wheat were identified. In both habitats Episyrphus balteatus was the most abundant species. Epistrophe spp. were only found in strips. No dependence of oviposition within wheat fields on the distance to the strips could be demonstrated. Due to their great mobility, it is easy for adult syrphids to find aphid colonies within a crop field. The strips are neither significant for an early development of the first syrphid generation nor for an additional generation after wheat harvest. The importance of herb strips for hoverflies lies in their quality to supply them with pollen and nectar, which increases the fitness of the adults.

Effects of elevated CO2 on flowering phenology and nectar production were studied in five important nectar plants of calcareous grasslands, i.e. Lotus corniculatus, Trifolium pratense, Betonica officinalis, Scabiosa columbaria and Centaurea jacea. Glasshouse experiments showed that flowering probability was significantly enhanced in C. jacea. B. officinalis flowered carlier and L. corniculatus produced more flowers under elevated CO2. In contrast, the number of flowers decreased in T. pratense. The amount of nectar produced per flower was not affected in the investigated legumes (T. pratense, L. corniculatus), but was significantly reduced in the other forbs. Elevated CO2 did not significantly affect nectar sugar concentration and sugar composition. However, S. columbaria and C. jacea produced significantly less total sugar per flower under elevated CO2. The nectar amino acid concentration remained unaffected in all investigated plant species whereas the total of amino acids produced per flower was significantly reduced in all non-legumes. In addition, the amino acid composition changed significantly in all investigated species except for C. jacea. The observed effects are unexpected and are a potential threat to flower visitors such as most butterflies which have no alternative food resources except nectar. Changes in nectar production due to elevated CO2 could also generally have detrimental effects on the interactions of flowers and their pollinators.

In animal farming, anthelmintics are regularly applied to control gastrointestinal nematodes. There is plenty of evidence that also non-target organisms, such as dung beetles, are negatively affected by residues of anthelmintics in faeces of domestic ungulates. By contrast, knowledge about possible effects on wild plants is scarce. To bridge this gap of knowledge, we tested for effects of the common anthelmintic formulation Cydectin and its active ingredient moxidectin on seed germination. We conducted a feeding experiment with sheep and germination experiments in a climate chamber. Three wide-spread plant species of temperate grasslands (Centaurea jacea, Galium verum, Plantago lanceolata) were studied. We found significant influences of both, Cydectin and moxidectin, on germination of the tested species. Across species, both formulation and active ingredient solely led to a decrease in germination percentage and synchrony of germination and an increase in mean germination time with the formulation showing a more pronounced response pattern. Our study shows for the first time that anthelmintics have the potential to negatively affect plant regeneration. This has practical implications for nature conservation since our results suggest that treatments of livestock with anthelmintics should be carefully timed to not impede endozoochorous seed exchange between plant populations.

Two naturally coexisting grassland species - Centaurea jacea (often predominating) and Fragaria vesca (subordinate) were grown together in a pot experiment of factorial design, where competition and arbuscular mycorrhiza (AM) inoculation were used as treatments. The effects of competition were one-sided, i.e. the mass of F vesca decreased relatively more than that of C. jacea as a result of competition. The root and total mass of C. jacea increased with AM inoculation while F vesca did not respond. The mass difference between C. jacea and F vesca in a particular pot increased when plants were mycorrhizal, mostly due to the mass increase of C. jaceae. This can be explained by the differential response of these species to AM. We did not find any indirect indication of the interplant transfer of resources. The results of this experiment show the more unbalanced competition (larger differences in biomass) resulting from AM infection of plants.

��� subsp. jacea Apr��s le subsp. grandiflora, il s���agit du taxon le moins rare en Corse. Insistons sur le fait qu����� part la tendance ��voqu��e �� propos de la sous-esp��ce pr��c��dente, le mat��riel de l�����le est relativement homog��ne, alors qu���en Belgique, en France continentale et ailleurs, des interm��diaires subsp. jacea ��� subsp. grandiflora se rencontrent ���� et l��., Published as part of Jeanmonod, Daniel & Schl��ssel, Andr��, 2012, Notes et contributions �� la flore de Corse, XXIV, pp. 293-321 in Candollea 67 (2) on page 305, DOI: 10.15553/c2012v672a11, http://zenodo.org/record/5777445

��� subsp. decipiens (Thuill.) Čelak. ��� Quenza, route de Zuro, prairie humide en contrebas, 28.7.1977, Desch��tres, R. s.n. (LG). Connu par la seule r��colte ci-avant, ce taxon est nouveau pourlaCorse et pr��sente un port assez diff��rent de celui des autres repr��sentants du groupe en Corse. Les feuilles sont en effet ��troitement lanc��ol��es (env. 5 mm de largeur) dans le bas de la plante et lin��aires plus haut, les bract��es inf��rieures sont pectin��es, les autres lacini��es �� subenti��res. Cela repr��sente une combinaison de caract��res unique en Corse. L�����chantillon est conforme �� divers exsiccata d���Europe continentale. Ce taxon est rep��rable par son port plus rameux et ses feuilles sup��rieures petites et ��troites, comme la subsp. angustifolia (= subsp. timbalii), mais les bract��es font ais��ment la diff��rence. Notons encore que des interm��diaires avec la subsp. timbalii existent sur le continent. J. LAMBINON, R. DESCH��TRES & J. GAMISANS, Published as part of Jeanmonod, Daniel & Schl��ssel, Andr��, 2012, Notes et contributions �� la flore de Corse, XXIV, pp. 293-321 in Candollea 67 (2) on page 306, DOI: 10.15553/c2012v672a11, http://zenodo.org/record/5777445

– subsp. grandiflora (Gaudin) Schübl. & Martens (= C. thuillieri (Dostál) J. Duvign. & Lambinon) C. thuillieri ne mérite que le rang de sous-espèce, à savoir C. jacea subsp. grandiflora (Gaudin) Schübl. & Martens; en effet, dans les travaux de référence cités ci-avant, ce taxon est réputé assez variable et les intermédiaires, en particulier avec la subsp. jacea, ne sont pas rares (c’est vrai en Belgique, dans NE de la France …). Il faut reconnaitre qu’en Corse, cette variabilité est réduite, portant essentiellement sur les bractées supérieures à appendice lacinié qui sont plus ou moins nombreuses et sur la coloration de la partie frangée de cet appendice, tendant à être plus claire que chez la subsp. jacea. Centaurea jacea subsp. grandiflora est le taxon le plus répandu en Corse et on peut encore ajouter les deux récoltes suivantes: – Secteur San Petrone, bords du Fium’Altu, 500 m en amont de Scatta Rumitoriu [42°25,04’N 9°23,42’E], rochers rive droite de la rivière, 230 m, 24.7.2011, Gamisans, J. s.n. (Hb. privé); sect San Petrone, haute Bravona, rive gauche, en amont du ruisseau de Sambuchettu, 1 km environ en amont de St Vincent, prairie de fauche humide, sursemée, 890 m, 14.7.2010, Gamisans, J. s.n. (Hb. privé).

��� subsp. angustifolia Gremli Deux ��chantillons sont rapport��s �� ce taxon dans les Compl. Prodr. Fl. Corse, loc. cit. Nous avons revu des doubles de ce mat��riel (env. de Ponte-Leccia et Ajaccio, Desch��tres, R. s.n. LG) et confirmons cette identit��. Ici se combinent, comme caract��res diagnostiques, des bract��es toutes lacini��es �� subenti��res et des feuilles ��troites, les sup��rieures ne d��passant pas 2-4 mm. Ces r��coltes (surtout celle d���Ajaccio) correspondent bien aux plantes du continent ainsi nomm��es; d���un point de vue nomenclatural toutefois, l�����pith��te �� angustifolia �� semble d���application incertaine, raison pour laquelle la �� Nouvelle Flore ��, loc. cit., utilise le nom C. jacea subsp. timbalii (Martrin-Donos) Br.- Bl. N��anmoins, on notera que GREUTER & VON RAAB- STRAUBE (Compositae. Euro+Med Plantbase, 2010 in http://www. emplantbase.org/home.html/ 27.6.2012) reconnaissent angustifolia et timbalii comme deux taxon infrasp��cifique diff��rents., Published as part of Jeanmonod, Daniel & Schl��ssel, Andr��, 2012, Notes et contributions �� la flore de Corse, XXIV, pp. 293-321 in Candollea 67 (2) on page 305, DOI: 10.15553/c2012v672a11, http://zenodo.org/record/5777445

These “notes” deal with 87 noteworthy taxa amongst which 14 are new to the island's flora. 3 of these taxa are native: Milium montianum, Rorippa palustris, Scleranthus annuus subsp. verticillatus and 8 are introduced: Centaurea jacea subsp. decipiens, Citrullus aff. colocynthis, Eleusine tristachya, Geranium sanguineum, Lampranthus brownii, Oenothera lindheimeri, Paspalum notatum, Vitis aff. labrusca and 3 were present in the past but have probably desappeared from the island: Camelina sativa subsp. microcarpa, Malcolmia maritima, Malcolmia triloba. The presence of Cuscuta suaveolens, Pelargonium graveolens, Ranunculus aquatilis, Sedum litoreum and Vicia narbonensis is once and for all confirmed. New localities are given on one hand for 32 taxa considered as “very rare” (RR) out of which 7 (Brassica rapa, Luzula sylvatica subsp. sieberi, Orchis mascula, Petroselinum crispum, Seseli djianeae, Trifolium phleoides subsp. audigieri and Veronica beccabunga) become “rare” (R). On the other hand 21 taxa considered to be “rare” (R) out of which 9 (Arum cylindraceum, Crassula vaillantii, Elymus caninus, Moenchia erecta subsp. erecta, Lathyrus annuus, Physospermum cornubiense, Scrophularia nodosa, Solanum villosum subsp. villosum and Vicia laeta) change their status from “rare” to “not common” (PF) or “localised” (LOC). Finally, the datas published for the 11 remaining taxa (considered “localised” (LOC)or “not common” (PF) taxa) constitute a considerable increase of our knowledge about their distribution. The new sites correspond often to a new sector for the presence of a given taxon. 14 of the whole lot of 88 taxa are part of the red list and 26 are xenophytic species. A distribution map is also provided for Crassula vaillantii, Platanthera algeriensis, Physospermum cornubiense and Vicia laeta.

Centaurea jacea L. s.l. Apr��s une analyse d��taill��e dans les Compl. Prodr. Fl. Corse, Asteraceae II (JEANMONOD & al.: 149-153 et 168-169, 2004), ce groupe a ��t�� trait�� de fa��on assez semblable dans Fl. Corsica (JEANMONOD & GAMISANS: 801-804, 2007). Ce qui frappe d��s l���abord est la s��paration au rang sp��cifique de Centaurea thuillieri de C. jacea, celui-ci repr��sent�� par deux sousesp��ces, �� savoir subsp. jacea et subsp. angustifolia. Ce syst��me est peu compatible avec divers travaux, dont celui de VANDERHOEVEN & al. (Plant Biol. 4: 403-412, 2002), base du nouveau traitement adopt�� par LAMBINON & al., Nouv. Fl. Belgique, Gd-Duch�� Luxembourg, N. France et R��g. Voisines, avec quelques mises au point nomenclaturales, qui devraient le cas ��ch��ant ��tre poursuivies (voir LAMBINON, Dumortiera 85-87: 32, 2005). L���examen de la majeure partie du mat��riel corse cit�� par JEANMONOD & al., loc. cit., 2004 et de quelques autres ��chantillons (surtout collect��s par R. Desch��tres) suscite les commentaires ci-apr��s., Published as part of Jeanmonod, Daniel & Schl��ssel, Andr��, 2012, Notes et contributions �� la flore de Corse, XXIV, pp. 293-321 in Candollea 67 (2) on page 305, DOI: 10.15553/c2012v672a11, http://zenodo.org/record/5777445

The article presents the results of research (2005-2011 years) of Centaurea jacea L. aсlonist large lifecycle. There are described in detail the age and stage of plant features. Widely covered the stages of shoot system formation.

Bioassay-guided fractionation of the chloroform extract of Centaurea jacea L. afforded the isolation of cirsiliol, apigenin, hispidulin, eupatorin, isokaempferide, axillarin, centaureidin, 6-methoxykaempferol 3-methyl ether, trachelogenin, cnicin, 4′-acetylcnicin and three aliphatic glucose diesters, including the new natural product 1β-isobutanoyl-2-angeloyl-glucose. The structures of the compounds were established on the basis of spectroscopic analyses (UV, MS and NMR). All compounds were isolated for the first time from this species. The compounds were evaluated for their tumour cell growth inhibitory activities on HeLa, MCF-7 and A431 cells. Different types of secondary metabolites (flavonoids, sesquiterpenes) were found to be responsible for the antitumour effects of the extracts; the highest activity was exerted by centaureidin, in addition to moderately active compounds (cirsiliol, isokaempferide, apigenin, hispidulin, cnicin and 4′-acetylcnicin).

Numerous species of the Asteraceae, the composites, are famous for their use in both traditional and conventional medicine. Reliable anatomical descriptions of these plants and of possible adulterations provide a basis for fast identification and cheap purity controls of respective medicinal drugs by means of light microscopy. Nevertheless, detailed comparative studies on root and rhizome anatomy of valuable as well as related inconsiderable composite plants are largely missing yet. The presented study aims to narrow this gap by performing anatomical analyses of roots and rhizomes of 16 species belonging to the tribe Cardueae, of formerly and currently used drugs as well as their near relatives as potential adulterations (Carlina acaulis L., Carlina vulgaris L., Arctium lappa L., Arctium tomentosum Mill., Carduus defloratus L., Carduus personata (L.) Jacq, Cirsium arvense (L.) Scop., Cirsium vulgare (Savi) Ten., Cirsium erisithales (Jacq.) Scop., Onopordum acanthium L., Silybum marianum (L.) Gaertn., Rhaponticum scariosum Lam., Centaurea jacea L., Centaurea scabiosa L., Centaurea cyanus L., Cnicus benedictus L.). A detailed verbal and graphical survey of the analysed anatomical features is provided. Several characters were finally extracted which allow for discrimination of the examined species and may be effectively used for drug quality controls.

Morphological plasticity of brown knapweed (Centaurea jacea L.) was examined. South bohemian populations of subsp. jacea were compared to plasticity in larger area. The plasticity of local population overlaps with both subspecies. The correlation between abiotical factors and determination characteristics were found. Molecular survey using ISSR method shows no difference between subspecies. The final resolution of subspecies existence will be questioned in following study.

Aims Invasion resistance in experimental plant communities is known to increase with increasing diversity and further to depend on the presence of particular functional groups. To test whether these effects also hold true for the invader establishment phase beyond the seedling stage, we studied survival and performance of Centaurea jacea L. (brown knapweecl) planted into experimental grassland communities of varying plant biodiversity over three consecutive years. Moreover, we analysed the role of insect herbivory and biomass of the recipient community for mediating diversity effects. Methods In 2005, seedlings of Centaurea were transplanted into experimental grassland communities (the Jena Experiment) covering a species richness (1-60) and functional group richness (1-4) gradient. Half of these transplants and the community surrounding them in each plot were sprayed with insecticide while the other half served as control. In 2006 and 2007 (during the second and third year after transplantation), we recorded survival, growth-related (e.g. transplant biomass, height) and reproduction-related traits (e.g. number of flower heads). Annual data on community aboveground biomass served as covariate to investigate mediating effects of aboveground competition with the recipient community. Important Findings Species richness was the most important factor responsible for Centaurea limitation. Higher levels of diversity decreased survival and all performance traits in both years. These diversity effects were partly driven by community biomass, but not fully explained by that covariate, suggesting the importance also of further processes. The influence of functional group richness was strong in the second year after transplantation and weaker in the third year. Among the particular functional groups, only the presence of legumes showed strong negative effects on Centaurea survival and weak negative effects on growth and reproduction, the latter two being mediated by biomass. Insect herbivore reduction considerably benefited Centaurea in sprayed monocultures, where it grew significantly larger than in all other diversity levels and than in the control subplots. We conclude that effects of plant community properties on invading individuals change in the course of establishment, that plant species richness effects are also important during later stages of establishment, and that biomass (especially at high diversity) and herbivory (especially at low diversity) of the recipient community are important in mediating community effects on invaders.

Cytogenetic analysis of several populations of Centaurea jacea (2n = 4x = 44), C. oxylepis (2n = 4x = 44) and C. phrygia (2n = 2x = 22) was performed using flow cytometry, differential chromosome staining and FISH. In all species Arabidopsis-type telomeric repeats hybridized only to the terminal part of chromosomes. In C. phrygia three pairs and in C. oxylepis six pairs of chromosomes revealed the hybridization signals of 45S rDNA. Centaurea jacea showed polymorphism in the 45S rDNA loci number, five or six pairs of sites were observed. 5S rDNA loci were located in two pairs of chromosomes in C. phrygia. In C. jacea and C. oxylepis the number and position of 5S rDNA loci were the same: three pairs located interstitially and one terminally. The genome size of the diploid C. phrygia was established as 2.14 pg/2C. The genomes of tetraploid species were nearly two times larger and genome size polymorphism was observed among C. jacea populations.

BACKGROUND: Agri-environment schemes play an increasingly important role for the conservation of rare plants in intensively managed agricultural landscapes. However, little is known about their effects on gene flow via pollen dispersal between populations of these species. METHODOLOGY/PRINCIPAL FINDINGS: In a 2-year experiment, we observed effective pollen dispersal from source populations of Centaurea jacea in restored meadows, the most widespread Swiss agri-environment scheme, to potted plants in adjacent intensively managed meadows without other individuals of this species. Potted plants were put in replicated source populations at 25, 50, 100 m and where possible 200 m distance from these source populations. Pollen transfer among isolated plants was prevented by temporary bagging, such that only one isolated plant was accessible for flower visitors at any one time. Because C. jacea is self-incompatible, seed set in single-plant isolates indicated insect mediated effective pollen dispersal from the source population. Seed set was higher in source populations (35.7+/-4.4) than in isolates (4.8+/-1.0). Seed set declined from 18.9% of that in source populations at a distance of 25 m to 7.4% at 200 m. At a distance of 200 m seed set was still significantly higher in selfed plants, indicating long-distance effective pollen dispersal up to 200 m. Analyses of covariance suggested that bees contributed more than flies to this long-distance pollen dispersal. We found evidence that pollen dispersal to single-plant isolates was positively affected by the diversity and flower abundance of neighboring plant species in the intensively managed meadow. Furthermore, the decline of the dispersal was less steep when the source population of C. jacea was large. CONCLUSIONS: We conclude that insect pollinators can effectively transfer pollen from source populations of C. jacea over at least 200 m, even when "recipient populations" consisted of single-plant isolates, suggesting that gene flow by pollen over this distance is very likely. Source population size and flowering environment surrounding recipient plants appear to be important factors affecting pollen dispersal in C. jacea. It is conceivable that most insect-pollinated plants in a network of restored sites within intensively managed grassland can form metapopulations, if distances between sites are of similar magnitude as tested here.

Centaurea jacea Linnaeus, Species Plantarum 2: 914. 1753. "Habitat in Europa septentrionali." RCN: 6606. Lectotype (Marsden-Jones & Turrill, Brit. Knapweeds: 14, pl. 2. 1954): Herb. Linn. No. 1030.36 (LINN). Current name: Centaurea jacea L. (Asteraceae). Note: Barbo & al. (in Taxon 47: 356. 1998) chose a Clifford sheet as type, unaware of the earlier choice made by Marsden-Jones & Turrill., Published as part of Jarvis, Charlie, 2007, Chapter 7: Linnaean Plant Names and their Types (part C), pp. 370-473 in Order out of Chaos. Linnaean Plant Types and their Types, London :Linnaean Society of London in association with the Natural History Museum on page 400, DOI: 10.5281/zenodo.291971

Centaurea jacea has been suggested as a potential bioindicator for ozone, but little is known about its intraspecific variation in sensitivity, especially at molecular level. The effects of ozone (200 ppb, 5 h) on sensitive and resistant lines of Centaurea have been investigated at the end of fumigation. Sensitive plants showed characteristic symptoms of injury in the form of diffuse discoloration stipples on leaves. A PCR-based approach was used to identify and isolate a partial-length cDNA coding for PAL and CHS genes. The northern analysis of PAL showed accumulation of transcript in both lines correlated with a typical increase of PAL activity (+41 and +91% in resistant and sensitive material, respectively, compared to controls). On the contrary, the transcripts of CHS, in resistant and sensitive plants, did not change after treatment. Total phenols were not affected by ozone, while anthocyanins were quickly utilised by resistant clone as antioxidant compounds.

Tropospheric ozone is a growing environmental menace in Italy and in the whole Mediterranean basin. The importance of active biomonitoring of this pollutant with hypersensitive Bel-W3 tobacco plants is stressed, and several examples of field studies carried out in Italy with this technique are presented. Current limitations are discussed, with special emphasis on data quality assessment and the opportunity of adopting easy-to-use kits based on tobacco germlings instead of adult plants. A standardization of methodologies (from cultivation to scoring and data elaboration), also at an international level, is strongly felt to be needed, in order to get official acknowledgement of biomonitoring procedures. Potential educational implications, with the active involvement of students and environmentalists, are shown. Other biological indicators are used, namely sensitive and resistant white clover (Trifolium repens) clones (as descriptors of biomass reduction in crops species) and Centaurea jacea (brown knapweed) as a model species to evaluate the relationship between ozone exposure and effects on the performance and injury symptoms of native plants which are largely used in the framework of European programmes.

Summary Sexual reproduction is important for the growth of populations and the maintenance of genetic diversity. Several steps are involved in the sexual reproduction pathway of plants: the production of flowers, the production of seeds and the establishment of seedlings from seeds. In this paper we quantify the relative importance and spatiotemporal variability of these different steps for four grassland perennials: Centaurea jacea , Cirsium dissectum , Hypochaeris radicata and Succisa pratensis . We compared undisturbed meadows with meadows where the top soil layer had been removed as a restoration measure. Data on the number of flower heads per flowering rosette, the numbers of flowers and seeds per flower head, and the seedling establishment probabilities per seed were collected by field observations and experiments in several sites and years. Combination of these data shows that H. radicata and S. pratensis have higher recruitment rates (1.9 and 3.3 seedlings per year per flowering rosette, respectively) than the more clonal C. dissectum and C. jacea (0.027 and 0.23, respectively). Seedling establishment is the major bottleneck for successful sexual reproduction in all species. Large losses also occurred due to failing seed set in C. dissectum . Comparison of the coefficients of variation per step in space and time revealed that spatiotemporal variability was largest in seedling establishment, followed closely by flower head production and seed set.

When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root¿shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context.

Ozone-sensitive (NC-S clone) and resistant plants (NC-R clone) of Trifolium repens and Centaurea jacea were exposed to moderate ozone concentrations in ambient air. The aim of this study was the investigation of the relation between ozone-sensitivity and leaf concentrations of antioxidants (ascorbic acid, total phenolics and total antioxidant capacity). NC-R clone showed the highest concentrations of antioxidants with 50–70% more ascorbic acid than NC-S. NC-R had about 5 times more ascorbic acid in the young leaves and 9 times more in the old leaves than Centaurea . In a fumigation experiment with acute ozone stress (100 nl L −1 ) the antioxidant levels changed profoundly. The ozone-injured leaves of NC-S had 6–8 times more total phenolics than uninjured leaves. Generally older leaves had lower antioxidant concentrations and were more prone to ozone injury than younger leaves. Ascorbic acid concentrations were closer related to the appearance of visible ozone injury than the other antioxidative parameters.