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In a clonal network, a mother plant is connected with daughter ramets. During network development, new ramets may encounter barriers that disrupt network integrity. As a result, resource allocation within a network is disturbed. In this study, the effect of network integrity disruption on the size of ramets and their sexual reproduction was investigated in mouse-ear hawkweed ( Hieracium pilosella ). Three types of networks were formed experimentally with unlimited resource allocation, with limited resource allocation between a mother plant and its daughter ramets and with limited resource allocation between all ramets. Networks were either supported by the presence of a mycorrhizal fungus or restricted by its absence. We found that the size of the mother and the effectiveness of sexual reproduction did not differ among network types. The length and dry mass of runners were higher in cases with limited resource exchange between a mother plant and its daughters. In the clonal plant network without any barriers to connection, a higher number of rosettes and lower dry mass of daughters were recorded. The mean number of daughter flowers did not differ among the network types. Mycorrhizal network is one of the most important factors for the sexual reproduction of clonal plants. With a reduced mycorrhizal network, plants invested in clonal growth.

In a clonal network, a mother plant is connected with daughter ramets. During network development, new ramets may encounter barriers that disrupt network integrity. As a result, resource allocation within a network is disturbed. In this study, the effect of network integrity disruption on the size of ramets and their sexual reproduction was investigated in mouse-ear hawkweed (Hieracium pilosella). Three types of networks were formed experimentally with unlimited resource allocation, with limited resource allocation between a mother plant and its daughter ramets and with limited resource allocation between all ramets. Networks were either supported by the presence of a mycorrhizal fungus or restricted by its absence. We found that the size of the mother and the effectiveness of sexual reproduction did not differ among network types. The length and dry mass of runners were higher in cases with limited resource exchange between a mother plant and its daughters. In the clonal plant network without any barriers to connection, a higher number of rosettes and lower dry mass of daughters were recorded. The mean number of daughter flowers did not differ among the network types. Mycorrhizal network is one of the most important factors for the sexual reproduction of clonal plants. With a reduced mycorrhizal network, plants invested in clonal growth. [ABSTRACT FROM AUTHOR]

Competition exerted by native plant communities is an important component of biotic resistance against the spread and impact of non-indigenous plant species in novel habitats. However, how the role of biotic resistance varies along environmental gradients to delay invasions is less clear. We conducted two field experiments to determine how competition from native communities affects colonization of a recognized invader of grasslands, Hieracium pilosella L., in the Fuegian steppe along different environmental gradients at regional and landscape scale. We assessed the role of competition on invader survival and growth along a climate gradient at regional scale (4.7–6.6 °C and 270–450 mm year−1), and across four major plant communities (i.e. meadows, grasslands, scrublands, and heathlands) along a topographic catena. At regional scale, the climate gradient showed a 33% reduction in H. pilosella survival at the coldest and wettest extreme, while reduced its biomass in 41% at the warmest and driest site, in the opposite extreme of the gradient. Competition caused a 34% decrease of the invader biomass, similarly along the climate gradient. At landscape scale, the topographic gradient had a stronger effect on invader survival reaching a 67% reduction in lowland meadows due to flooding events, while competition reduced in 29–39% the invader biomass only in grasslands or scrublands with negligible effects on low-resource heathlands. These results suggest that biotic resistance plays a significant and similar role along the climate gradient to delay invasion at regional scale, but at landscape scale is only determinant for rich-resource communities in absence of abiotic stresses. [ABSTRACT FROM AUTHOR]

The study of invasion patterns across multiple spatial scales brings insight about the spread of exotic species in novel habitats. We examined the spatial patterns of yellow mouse-ear hawkweed (Hieracium pilosella L.), a recognized invader plant in Tierra del Fuego rangelands, at the scales of landscape and vegetation stand to assess the roles of disturbance, propagule pressure and biotic drivers. We surveyed twenty plots along two transects (ca. 20 km) across paddocks with different disturbance history (degraded pastures vs. natural communities) and at increasing distances from invasion hotspots. We analyzed the patterns of density, cover, and size structure of local H. pilosella populations across the landscape scale, and we conducted point- and mark-pattern analyses of distribution of patches of this species within vegetation stands. At landscape scale, the hawkweed density and cover decreased from west to east only in the transect including degraded pastures in the western portion. Plots located within 7 km or less from degraded pastures exhibited higher cover of H. pilosella (5–10%) than plots farther away (< 0.1%). Local populations inside or near the degraded pastures exhibited higher frequency of large patches than populations located farther away. At the scale of vegetation stand, point-pattern analysis detected aggregation of H. pilosella patches at short distances (0.5–3 m) in most plots; whereas, in highly infested plots, mark-correlation function analysis indicated a negative association between the sizes of patches located at short distances (0.5–1.5 m) from each other. Human disturbance, propagule pressure originating in invasion hotspots, and long-distance dispersal events appear as determinants of the spread of H. pilosella invasion at landscape scale. At patch scale, field patterns suggest that local encroachment is mostly determined by vegetative growth and somehow limited by interference from large established hawkweed patches. Our results strongly suggest that, unless effective management actions are taken, over the near future (30–50 years) the exotic forb H. pilosella will continue to invade displacing the native shrub steppe and grassland vegetation in the region. [ABSTRACT FROM AUTHOR]

The symbiosis of plants with arbuscular mycorrhizal fungi (AMF) may become parasitic if the cost:benefit ratio (carbon:phosphorus ratio) increases. In case of mycorrhizal parasitism, a plant may prevent growth depression through the reduction of root colonization as a form of control over the symbiosis. In this greenhouse study, we attempted to manipulate the cost:benefit ratio of the arbuscular mycorrhizal symbiosis by shading and/or phosphorus (P) fertilization in the differentially mycotrophic plant species Hieracium pilosella and Corynephorus canescens. By repeated sampling of soil cores, we assessed the temporal progress of plant investment towards mycorrhizal structures as a measure of plant control over the AMF. Unexpectedly, we found no obvious treatment effects on mycorrhizal growth dependency (MGD), most likely caused by constant N-limitation in AM plants being enhanced by P-fertilization and shade probably not exacerbating plant C-budget for AMF. This highlights the importance of N:P:C stoichiometry for the outcome of the symbiosis. Nevertheless, we found possible control mechanisms in shaded H. pilosella, with considerably higher resource investments into root than into hyphal growth, while root colonization was only marginally suppressed. This control only manifested after 4 weeks of growth under potentially detrimental conditions, emphasizing the importance of time in plant control over the arbuscular mycorrhizal symbiosis. In contrast, the less mycotrophic C. canescens did not exhibit obvious changes in mycorrhizal investments in reaction to shading and P-fertilization, possibly because the low mycotrophy and AMF colonization already imposes a functioning control mechanism in this species. Our study suggests that highly mycotrophic plants may have a stronger need to keep AMF in check than less mycotrophic plants, which may have implications for the role of mycotrophy in the outcome of symbiotic interactions in natural situations. [ABSTRACT FROM AUTHOR]

Plants usually interact with other plants, and the outcome of such interaction ranges from facilitation to competition depending on the identity of the plants, including their sexual expression. Arbuscular mycorrhizal (AM) fungi have been shown to modify competitive interactions in plants. However, few studies have evaluated how AM fungi influence plant intraspecific and interspecific interactions in dioecious species., The competitive abilities of female and male plants of Antennaria dioica were examined in a greenhouse experiment. Females and males were grown in the following competitive settings: (i) without competition, (ii) with intrasexual competition, (iii) with intersexual competition, and (iv) with interspecific competition by Hieracium pilosella - a plant with similar characteristics to A. dioica. Half of the pots were grown with Claroideoglomus claroideum, an AM fungus isolated from the same habitat as the plant material. We evaluated plant survival, growth, flowering phenology, and production of AM fungal structures., Plant survival was unaffected by competition or AM fungi. Competition and the presence of AM fungi reduced plant biomass. However, the sexes responded differently to the interaction between fungal and competition treatments. Both intra- and interspecific competition results were sex-specific, and in general, female performance was reduced by AM colonization. Plant competition or sex did not affect the intraradical structures, extraradical hyphae, or spore production of the AM fungus., These findings suggest that plant sexual differences affect fundamental processes such as competitive ability and symbiotic relationships with AM fungi. [ABSTRACT FROM AUTHOR]

Interactions of plants with arbuscular mycorrhizal fungi (AMF) may range along a broad continuum from strong mutualism to parasitism, with mycorrhizal benefits received by the plant being determined by climatic and edaphic conditions affecting the balance between carbon costs vs. nutritional benefits. Thus, environmental conditions promoting either parasitism or mutualism can influence the mycorrhizal growth dependency (MGD) of a plant and in consequence may play an important role in plant-plant interactions.In a multifactorial field experiment we aimed at disentangling the effects of environmental and edaphic conditions, namely the availability of light, phosphorus and nitrogen, and the implications for competitive interactions between Hieracium pilosella and Corynephorus canescens for the outcome of the AMF symbiosis. Both species were planted in single, intraspecific and interspecific combinations using a target-neighbor approach with six treatments distributed along a gradient simulating conditions for the interaction between plants and AMF ranking from mutualistic to parasitic.Across all treatments we found mycorrhizal association of H. pilosella being consistently mutualistic, while pronounced parasitism was observed in C. canescens, indicating that environmental and edaphic conditions did not markedly affect the cost:benefit ratio of the mycorrhizal symbiosis in both species. Competitive interactions between both species were strongly affected by AMF, with the impact of AMF on competition being modulated by colonization. Biomass in both species was lowest when grown in interspecific competition, with colonization being increased in the less mycotrophic C. canescens, while decreased in the obligate mycotrophic H. pilosella. Although parasitism-promoting conditions negatively affected MGD in C. canescens, these effects were small as compared to growth decreases related to increased colonization levels in this species. Thus, the lack of plant control over mycorrhizal colonization was identified as a possible key factor for the outcome of competition, while environmental and edaphic conditions affecting the mutualism-parasitism continuum appeared to be of minor importance.

The fraction of sterol acetates from the inflorescences of Hieracium pilosella has been isolated in the typical way from petroleum ether extract. By means of the weight method the total amount of sterols was determined (0.2659%). The mixtures of sterol acetates and free sterols were investigated using GC-MS techniques. The occurrence of about 18 sterols has been observed. Cholesterol, cholest-8(14)-en-3b-ol, cholesta-5.7-dien-3b-ol, cholest-7-en-3b-ol, ergosta-5.24-dien-3b-ol, campesterol, stigmasterol, b-sitosterol, fucosterol, 5a-stigmast-7-en-3a-ol were identified. The probable structures of lophenol, isofucosterol, 5a-stigmasta-7.24-dien-3b-ol, lanosta-9(11).24-dien-3b-ol and 24-ethylidene lophenol were stated on the basis of literature data. The last 4 sterols occur in a vestigial quantity, which made its identification impossible. Sitos erol and cholesterol are remarkably dominating sterols in the fraction.

Typical chromatographic methods were successfully applied to isolate nine flavonoid compounds and two coumarin glycosides from the inflorescences and the herb of Hieracium pilosella L. Repeated column chromatography, occasionally paper chromatography and recrystallization made the separation of three flavonoid aglycones and six glycosides - possible. Coumarin glycosides were isolated by preparative thin layer chromatography. Subsequent UV, NMR and MS analyses have led to identification of the following flavonoid derivatives: known for the species - apigenin, luteolin, luteolin 7-O- ß-glucopyranoside, luteolin 4’-O-ß-glucopyranoside, isoetin 7-O-ß- -glucopyranoside, isoetin 4’-O-ß-glucuronide and new for the species – kaempferol 3-methyl ether and apigenin 7-O-ß-glucopyranoside. Third isoetin glycoside contained two different sugar moieties: xylose and glucose, probably attached to the hydroxyl groups at C-4’ or C-4’ and C-2’(or 5’) of an aglycone. Umbelliferone 7-O-ß-glucopyranoside (skimmin) and new for the genus Hieracium esculetin 7-O-ß-glucopyranoside (cichoriin) were determined by NMR and MS methods.

Interactions of plants with arbuscular mycorrhizal fungi (AMF) may range along a broad continuum from strong mutualism to parasitism, with mycorrhizal benefits received by the plant being determined by climatic and edaphic conditions affecting the balance between carbon costs vs. nutritional benefits. Thus, environmental conditions promoting either parasitism or mutualism can influence the mycorrhizal growth dependency (MGD) of a plant and in consequence may play an important role in plant-plant interactions. In a multifactorial field experiment we aimed at disentangling the effects of environmental and edaphic conditions, namely the availability of light, phosphorus and nitrogen, and the implications for competitive interactions between Hieracium pilosella and Corynephorus canescens for the outcome of the AMF symbiosis. Both species were planted in single, intraspecific and interspecific combinations using a target-neighbor approach with six treatments distributed along a gradient simulating conditions for the interaction between plants and AMF ranking from mutualistic to parasitic. Across all treatments we found mycorrhizal association of H. pilosella being consistently mutualistic, while pronounced parasitism was observed in C. canescens, indicating that environmental and edaphic conditions did not markedly affect the cost:benefit ratio of the mycorrhizal symbiosis in both species. Competitive interactions between both species were strongly affected by AMF, with the impact of AMF on competition being modulated by colonization. Biomass in both species was lowest when grown in interspecific competition, with colonization being increased in the less mycotrophic C. canescens, while decreased in the obligate mycotrophic H. pilosella. Although parasitism-promoting conditions negatively affected MGD in C. canescens, these effects were small as compared to growth decreases related to increased colonization levels in this species. Thus, the lack of plant control over mycorrhizal colonization was identified as a possible key factor for the outcome of competition, while environmental and edaphic conditions affecting the mutualism-parasitism continuum appeared to be of minor importance. [ABSTRACT FROM AUTHOR]

Background and Aims: Root segregation has been observed in a variety of species. Though it is usually attributed to a plant's attempt to avoid below ground competition, a direct correlation of root distribution with the intensity of competition has never been shown. Methods: The test species Hieracium pilosella L. was exposed to a gradient of competitive pressure using the closely related species Arabidopsis petraea (L.) V.I.D OROF., Arabidopsis thaliana (L.) Heynh ., Capsella rubella Reut . and Cardamine hirsuta L. as neighbouring plants. Horizontal root distribution was quantified using a soil monolith method. Results: The neighbour species could be ranked according to their competitive effect on the test species, identifying two weak ( A. thaliana and A. petraea) and two strong competitors ( C. hirsuta and C. rubella). The degree of root segregation correlated negatively with the competitive effect caused by the various neighbour species. Conclusions: We conclude that root segregation is indeed a response to competitive pressure. Further factors such as root symbiotic relationships or root exuded allelochemicals are supposedly involved in the outcome of root interactions. We propose the use of screening experiments on root responses to various neighbours in order to quantify each factor's relative influence on rooting patterns. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) may serve as an effective substitute for root surface. As mycorrhizal benefits are related to nutrient availability, the trade-off between carbon investments into AMF versus roots may drive competitive interactions. We studied competitive interactions between mycorrhizal and non-mycorrhizal individuals of Hieracium pilosella L. and Plantago lanceolata L., species differing in both mycotrophic degree and carbon allocation to roots. Three fertilization treatments were used to simulate nutritional differences over the course of succession. Species-specific differences in mycotrophy were reflected in markedly larger root/shoot allocation in P. lanceolata and higher mycorrhizal growth dependency in H. pilosella. P. lanceolata dominated competition in all fertilizer treatments, enabled by its comparatively larger root biomass allocation. In contrast, under intermediate and high fertilization, H. pilosella exhibited large investments into clonal shoot growth rather than in roots. Unexpectedly, the competitive imbalance between both species was amplified by the presence of AMF. The poor competitive strength of H. pilosella indicates that AMF-dominated foraging can be less effective than root-dominated foraging in competitive interactions, particularly under high nutrient availabilities. However, the competitive imbalance was reduced in favor of H. pilosella under nutrient deficiency. Our results lend support to the idea of differing competitive success of mycorrhizal- versus root-based foraging strategy over a nutritional gradient, which may play a role in the natural distribution of species over the course of succession. [ABSTRACT FROM AUTHOR]

Root-root interactions are much more sophisticated than previously thought, yet the mechanisms of belowground neighbor perception remain largely obscure. Genome-wide transcriptome analyses allow detailed insight into plant reactions to environmental cues. A root interaction trial was set up to explore both morphological and whole genome transcriptional responses in roots of Arabidopsis thaliana in the presence or absence of an inferior competitor, Hieracium pilosella. Neighbor perception was indicated by Arabidopsis roots predominantly growing away from the neighbor (segregation), while solitary plants placed more roots toward the middle of the pot. Total biomass remained unaffected. Database comparisons in transcriptome analysis revealed considerable similarity between Arabidopsis root reactions to neighbors and reactions to pathogens. Detailed analyses of the functional category "biotic stress" using MapMan tools found the sub-category "pathogenesis-related proteins" highly significantly induced. A comparison to a study on intraspecific competition brought forward a core of genes consistently involved in reactions to neighbor roots. We conclude that beyond resource depletion roots perceive neighboring roots or their associated microorganisms by a relatively uniform mechanism that involves the strong induction of pathogenesis-related proteins. In an ecological context the findings reveal that belowground neighbor detection may occur independently of resource depletion, allowing for a time advantage for the root to prepare for potential interactions [ABSTRACT FROM AUTHOR]

Abstract: Intensity of ultraviolet-B radiation (UV-B) differs between northern and southern hemispheres. Therefore, exotic plants species that originate from the northern hemisphere provide an opportunity to study the effects of UV-B on plant physiology and growth, and their implications for the role of adaptation and phenotypic plasticity during plant invasion on the southern hemisphere. We conducted a growth-chamber experiment with and without UV-B on Hieracium pilosella plants from Germany, where the species occurs natively and New Zealand (NZ), where it is invasive. We tested the hypothesis that: (i) H. pilosella plants respond to UV-B with high phenotypic plasticity, demonstrating the ability to react to changes in UV-B, and (ii) NZ plants are better adapted to UV-B than German plants as a result of directional selection of well adapted phenotypes. Consistent with our first hypothesis H. pilosella plants reacted plastically to UV-B by producing longer foliar hairs and a higher leaf dry matter content (LDMC) when they were treated with UV-B regardless of their origin. Additionally, irrespective of the treatment, plants from NZ displayed a higher LDMC and grew less but longer leaves than German plants. Plants showed typical stress responses and a reduction in growth caused by the UV-B treatment: below-ground biomass and production of ramets were reduced when plants were treated with UV-B. H. pilosella proved to be particularly well predisposed to grow in areas of high UV-B radiation. Our findings hint at the necessity to consider UV-B radiation in future research on mechanisms of invasions in regions with high UV-B irradiation. Species that provide the ability to respond directly to UV-B might have an advantage to invade these areas. As UV-B intensity is likely to change in the future due to ongoing ozone depletion, research addressing the effects of UV-B during plant invasions is of increasing importance. [Copyright &y& Elsevier]

Within a population of invasive Hieracium pilosella in Chilean Patagonia we found two ploidy levels, pentaploid and hexaploid. Each ploidy level was represented by one clone. Their reproductive system was apomictic (and thus replicating the maternal genome), with a low degree of residual sexuality. It is necessary to prevent the evolution of new biotypes via hybridisation with different clones of H. pilosella or other Hieracium species introduced into Patagonia. [ABSTRACT FROM AUTHOR]

Studying patterns of species invasions over time at multiple spatial scales may help us to elucidate important factors driving those patterns and how they change according to temporal or spatial resolution. Here we provide a large, long-term, landscape-scale study of the invasion of three Hieracium species using a dataset that encompasses vegetation change on 124 transects over 25 years across the lower eastern South Island of New Zealand. We investigated the relationships between key environmental and ecological factors and the invasion trajectories of H. lepidulum, H. pilosella and H. praealtum, at two spatial scales: (i) among-transect colonization and (ii) within-transect changes in frequency and per cent cover. Our results show that the colonization and spread of Hieracium species among and within transects reflect (i) the importance of initial environmental and biological conditions, (ii) that our sampling captured different periods of the invasion trajectories of each of the three species, and (iii) the effects of differences in life histories of the three species. [ABSTRACT FROM AUTHOR]

The germination stage is critical in plant life-history and is also a key process during the expansion of species' ranges into new environments. In this study we investigated the germination patterns of three plant species ( Achillea millefolium, Hieracium pilosella and Hypericum perforatum) that are invasive to New Zealand (NZ) and native to Central Europe. We asked whether the species show differences in germination temperature requirements, germination speed and maximum germination rates, and thus, whether they display evidence of adaptation to different conditions in the invasive range. Seeds from three populations per species and region were subjected to three different temperature regimes to compare germination rates among origins and across temperature conditions. For Achillea millefolium and Hypericum perforatum, germination rates were significantly higher for invasive NZ provenances than for native German ones. Seeds from invasive populations of all three species displayed increased maximum germination at medium temperature conditions when compared to native populations, which indicates altered germination strategies in the invaded range. Changes in temporal development patterns were most conspicuous for invasive Hieracium pilosella and Hypericum perforatum populations. These findings imply that adaptation in germination patterns towards different climatic conditions in invasive populations has occurred. Our study emphasises the importance of the germination stage during plant invasion and its role in explaining range expansion of these species. [ABSTRACT FROM AUTHOR]

1. The distribution and abundance of invasive species can be driven by both environmental variables and land management decisions. However, understanding these relationships can be complicated by interactions between management actions and environmental variability, and differences in scale among these variables. The resulting ‘context-dependence’ of management actions may be well-appreciated by ecologists and land managers, but can frustrate attempts to apply general management principles. 2. In this study, we quantify the effects of land management and environmental variability at different scales on the occurrence and abundance of Hieracium pilosella, a major agricultural weed in New Zealand. We used a hierarchical study design and analysis to capture relevant scales of variation in management actions and environmental heterogeneity, and test hypotheses about how these factors interact. 3. We show that fertilizing and grazing interact with environmental gradients at the scale of management application (farm paddocks) to influence the establishment and local abundance of H. pilosella. 4. We further show that H. pilosella’s relationships with fine-scale abiotic and biotic factors are consistent with expected mechanisms driven by larger-scale management actions. Using data on occurrence and local abundance, we tease apart which factors are important to establishment and subsequent local spread. 5. Synthesis and applications. A major challenge for environmental scientists is to predict how invasive species may respond to ongoing landscape modifications and environmental change. This effort will require approaches to study design and analysis that can accommodate complexities such as interacting management and environmental variables at different scales. Management actions will be more likely to succeed when they explicitly account for variation in environmental context. [ABSTRACT FROM AUTHOR]

Aim Our aim was to test for changes in growth patterns of three clonally growing plant species ( Achillea millefolium, Hieracium pilosella and Hypericum perforatum) between native and invaded regions. We addressed the hypotheses that with differing important life-history traits, invasive populations perform better than native populations, and that this expected better performance is linked to weakened trade-offs between individual growth and sexual and clonal reproduction. Location Germany and New Zealand. Methods We conducted field surveys for the three above-mentioned species in both native German and invasive New Zealand populations, and collected data at both population and individual levels. Results At the population level, the proportion of flowering plants, population size and population density were all higher in invasive populations. Similarly, at the individual level, the number of stolons per plant, stolon–biomass ratio and population crowdedness (local plant density in a specified area around a target plant) were significantly higher in New Zealand. Plant height did not differ between countries, and plant biomass was lower in New Zealand than in Germany for Achillea millefolium and Hypericum perforatum. These two species showed significant trade-offs between individual growth and sexual and clonal reproduction. Achillea millefolium exhibited a weakened trade-off in its invaded range, where the same proportion of flowering plants was sustained at much higher levels of population crowdedness than in its native range. Main conclusions The apparent invasion success of the three study species is generally due to better overall performance in their respective invaded ranges. In respect of both Achillea millefolium and Hypericum perforatum, this is driven primarily by increased vegetative reproduction. In contrast, Hieracium pilosella seems to benefit more from increased sexual reproduction in its invaded range. Shifts in trade-offs as a general trend seem to be of minor importance. [ABSTRACT FROM AUTHOR]

1 We tested the hypothesis that the competitive effect of multi-species mixtures on a single target plant can be described as a simple additive function of the effects of single species. 2 In a controlled field competition experiment on sand, we used four common species of dry acidic grasslands ( Hieracium pilosella, Jasione montana, Corynephorus canescens and Festuca ovina) to study the effects of both, single- and multi-species neighbourhoods on the target species H. pilosella. 3 Target plant biomass points at a competitive ranking of neighbour species with F. ovina as the strongest competitor followed by C. canescens and H. pilosella, while J. montana has a lower effect on the target. The analysis of the competitive response gives no indication of competitive release or amplification with increasing number of neighbouring species. 4 Further analysis with yield-density models reveals that the competition intensity of most multi-species mixtures is well predicted by the effect of pairwise interactions. Hence, for the majority of species combinations, our results indicate additive effects of species competition. 5 Specific species combinations, however, significantly deviate from this result. For combinations of C. canescens with either one of the herbs, the models show a significantly better fit if a non-additivity parameter is included. The important missing factor to describe target plant growth is species-specific biomass of neighbouring plants and here root biomass is the most crucial determinant. The addition of each of these factors as non-additive parameters significantly increases the predictive power of the model. 6 Our work adds to the increasing evidence that interactions in diverse plant communities are not simply a sum of their component species interactions. For a better understanding of the effect of competition on the structure and development of diverse plant communities, future studies need to consider both additive and non-additive effects of competing species. [ABSTRACT FROM AUTHOR]

Sleeper weeds, a relatively new concept, are defined as a sub-group of invasive plant species for which their population sizes are known to have increased significantly more than 50 years after they became naturalized. The invasions of the European herb Hieracium pilosella into New Zealand, the northeast Asian Fallopia japonica and the Sicilian Senecio squalidus into Britain are presented as well-documented examples of sleeper weeds. While the concept of sleeper weeds has gained some acceptance with weed managers, its application remains a retrospective activity at present. Genetic factors, environmental suitability and anthropogenic disturbance are discussed as they affect sleeper weed status. Accurate botanical records for invasive species over long periods of time are relatively rare and limit documentation of the phenomenon. Some mathematical and ecological problems remain with the concept and its wider application to weed invasion, including the adequacy of the species level for determining sleeper weed status in genetically diverse and widely distributed groups of invasive plants. [ABSTRACT FROM AUTHOR]

Foliar sprays of different nitrogen compounds promoted rather than inhibited Hieracium pilosella in the weeks following spray application on undeveloped tussock grassland. Continued annual granular applications promoted general vegetation growth to the detriment of H. pilosella in the absence of grazing. Single applications of boron at high rates had specific adverse effects on H. pilosella for up to 4-5 years, and possibly promotive effects on shortterm grasses. [ABSTRACT FROM AUTHOR]

This paper presents the results of an assessment of the concentration of these heavy metals Fe, Mn, Zn, Pb, Cu, Ni and Cd in leaves, rhizomes and roots of Hieracium pilosella L,, as well as in soils from its habitats within the Wieluń area. The levels of the heavy metals in the soils were low and within the geochemical background. Thus, they might be considered natural. Higher content of the heavy metals in mouse-ear hawkweed leaves and roots as compared to the background values revealed its accumulative properties. Higher content of all the heavy metals studied was found in rhizomes and roots of/-L pilosella as compared to leaves, with the exception of Cd, which accumulated more effectively in the underground organs. [ABSTRACT FROM AUTHOR]

Abstract: Crepis capillaris, Hieracium pilosella, and Hypochaeris radicata were investigated for the influence of the altitude of the collection site on the content of phenolics within the flowering heads. These three taxa from the Lactuceae tribe of the Asteraceae family originate from Europe and are now widespread within New Zealand. Flowering heads collected from different altitudes ranging from 180m to 1060m (C. capillaris), from 190 to 1290m (H. pilosella), and from 20m to 1290m (H. radicata), respectively, were extracted and analysed by high performance liquid chromatography. Results showed a positive correlation between the altitude of the growing site and the contents of flavonoids and phenolic acids for all investigated taxa. The altitudinal effect was, however, partially concealed by geographic differences between coastal and inland collection sites, with the inland collections containing higher concentrations of flavonoids and phenolic acids than plants collected from the coast. The results are discussed in the light of a putative UV-B protective function of the quantified compounds and of the immigration histories of the three species at hand. [Copyright &y& Elsevier]

We used a spatially explicit simulation model to examine the relative importance of vegetative and sexual reproduction in Hieracium pilosella L. Based on an understanding of the complex life cycle of this species and on data from in situ population dynamics in a calcareous grassland in NW Switzerland, we simulated growth and the relative contribution of clonal reproduction by stolons and reproduction by seeds across a gradient of increasing soil fertility. Competition by a clonal grass resulted in nearly complete exclusion of H. pilosella from the more fertile part of the simulation plot. Under low soil fertility, when grass could not survive, H. pilosella largely persisted by vegetatively produced rosettes. This pattern of a sharp separation of both species was shifted slightly in favour of H. pilosella by introducing random disturbances. Only by adding: (1) long‐distance seed dispersal, and (2) facilitation of seedling establishment in the vicinity of grass tussocks in vegetation gaps was a more realistic representation of field observations realised, with rosettes of H. pilosella grown from seeds occasionally distributed within dense grass vegetation. Phenotypic plasticity of stolon length was a decisive factor for the maintenance of H. pilosella populations. We conclude that a mixed strategy of clonal growth and reproduction by seeds in H. pilosella is necessary to maintain populations of this species in the presence of high interspecific competition and a shortage of open space. [ABSTRACT FROM PUBLISHER]

Summary: In two experiments, we tested whether species specific traits or mainly biomass determines the competitive strength of plant individuals in resource-poor habitats. As measure of competition intensity, we calculated the log Response Ratio (lnRR) based on total biomass for three key species of early successional stages on inland dunes. Using seedlings of Corynephorus canescens and Hieracium pilosella in a pot experiment, competition intensity was significantly and positively correlated with the biomass of the respective competitors. In contrast, such a correlation was not detected in a controlled field experiment with adult plants of the two species and of Carex arenaria. However, in both experiments the strength of competitive interactions (measured as lnRR) significantly depended on the identity of the competing species. We conclude, that a biomass advantage over the competitors (which can for instance be achieved by earlier germination) seems to play a crucial role only for successful seedling establishment, while competitive interactions of neighbouring plants depend on species-specific biomass allocation strategies at both developmental stages. Um zu testen, ob artspezifische Eigenschaften oder hauptsächlich die Biomasse selbst die Konkurrenzstärke zwischen Pflanzen auf ressourcenarmen Standorten bestimmen, wurde der Log Response Ratio (lnRR) der Gesamtbiomasse für drei dominante Arten früher Sukzessionsstadien auf Sand bestimmt. In einem Topfexperiment, in dem Keimlinge der Arten Corynephorus canescens und Hieracium pilosella verwendet wurden, nahm die Konkurrenz mit zunehmender Biomasse umgebender Keimlinge signifikant zu. In einem zweiten Experiment unter kontrollierten Freilandbedingungen, dagegen, in dem ausgewachsene Pflanzen der gleichen Arten zusammen mit Carex arenaria gemessen wurden, war die Konkurrenzintensität nicht signifikant von der Biomasse benachbarter Pflanzen abhängig. Artspezifische Eigenschaften hatten jedoch einen signifikanten Einfluss auf die Konkurrenzstärke sowohl von Keimlingen als auch von älteren Pflanzen. Wir folgern daraus, dass ein zeitlicher Vorsprung bei der Besiedlung offener Flächen, der mit höherer Biomasse einher geht, für einen Keimling einen entscheidenden Konkurrenzvorteil bietet. Mit zunehmendem Alter jedoch nimmt der Einfluss der Biomasse auf das Konkurrenzgeschehen ab und die artspezifische Biomasse-Allokation gewinnt mehr und mehr an Bedeutung. [Copyright &y& Elsevier]

Abstract Radiation of adventive, sexually reproducing organisms into a new environment has been well documented, but less is understood about the patterns and processes of geographical radiation in adventive species with uniparental reproduction (parthenogenesis or apomixis), usually associated with ‘frozen’ variation within maternal lineages. In this study we have used Pilosella officinarum to test the hypothesis that sexual reproduction becomes important in the radiation of adventive facultatively apomictic species. Within its native Europe P. officinarum is an extremely variable species, with eight subspecies and a range of ploidy levels. Pentaploids are always apomictic. However, early chromosome analyses of New Zealand adventive populations, carried out during the 1980s, discovered only pentaploid, apomictic clones. Similar observations were made in an early 1990s study of the same sites. Since then, a range of ploidy levels, including aneuploids, and a plethora of morphological variation, has been recorded. In this paper, we use a combination of image analysis and chromosome counts to show that sexual reproduction has become an important avenue for adaptive radiation in New Zealand populations of P. officinarum. Current populations probably comprise complex among-subspecies hybrids, and possibly among-species hybrids, which are at least partially capable of sexual reproduction and various forms of back-crossing. Somatic mutation may also play an important role in creating morphological variation. DNA fingerprinting did not contribute to this study because this technique failed to distinguish between morphological types observed in the field. [ABSTRACT FROM AUTHOR]

On colliery heaps in northern France, a tall grassland community dominated by Arrhenatherum elatius, give place to a thin grassland community in which Hieracium pilosella is very abundant. It has been claimed that Hieracium pilosella is an allelopathic species and this phenomenon has been investigated as an explanation of this phase of plant succession. The importance of osmotic pressure in tested plant extracts is demonstrated and may be responsible for presumed allelopathy. Two phytotoxic compounds have been revealed in roots+rhizomes of Hieracium pilosella (umbelliferon and apigenin-glucoside). A third phytotoxic compound was exuded by roots in hydroponic cultures (7-glucoside-umbelliferon or skimin). However no toxicity of soil has been found and no phytotoxic compounds appeared to be present in the soil under Hieracium pilosella. Experimental mixed cultures (sterile or non-sterile conditions) reveal suppression of Hieracium pilosella by Arrhenatherum elatius rather than the reverse. Allelopathy cannot be invoked to explain this plant succession. [ABSTRACT FROM AUTHOR]