Growth Tolerance of Rhizobia Isolated from Sand Dune Legumes of the Southwest Coast of India

This paper describes the properties of rhizobia from extreme soil environments which are characterized by high temperatures, salt concentrations and also rather extreme pH values due to the contamination by spray water from the sea. Coastal sand dunes are such extreme habitats which support a variety of microorganisms. To explore stress‐tolerant rhizobia, ten rhizobial strains were isolated from five wild legumes from two dune systems of the southwest coast of India. They were tested for growth performance or tolerance at a wide range of temperatures (30–55 °C), salinity (0.1–4.5 % w/v) and initial pH values (3.5–11). Growth of five isolates was highest between 30–40 °C, while four isolates showed considerable growth up to 2.5 % salinity (at 35 °C). All isolates demonstrated elevated growth at an initial pH of between 5–6 (at 35 °C and 2 % salinity), while five isolates had additional growth peaks at an initial pH of between pH 7.5–9 indicating alkaline tolerance and were suitable for efficient phosphate solubilization. The stress tolerance traits of these rhizobia are of potential value for strain improvement in agriculture or the bioremediation of soils at elevated temperatures, salinity and extreme pH values, and thus are of high biotechnological importance.     

Relationships Among Rhizobia from Native Australian Legumes

Isolates from 12 legumes at three sites in Victoria showed a wide range of morphological, cultural, symbiotic, and serological properties. Isolates from Acacia longifolia var. sophorae and Kennedia prostrata were fast growing but nodulated ineffectively Macroptilium atropurpureum and all native legumes except Swainsonia lessertiifolia. Isolates from S. lessertiifolia showed anomalous properties intermediate between fast- and slow-growing rhizobia. All isolates from the other two sites were slow-growing “cowpea” rhizobia. Symbiotic effectiveness was usually poor, and there was no relationship between effectiveness and host taxonomy or serological affinities of the isolates. This is the first report of fast-growing rhizobia from temperate Australian woody legumes and the first report of the symbiotic effectiveness of native Australian legumes with indigenous rhizobia.     

Rhizobial hitchhikers from Down Under: invasional meltdown in a plant–bacteria mutualism?

Aim This study analysed the diversity and identity of the rhizobial symbionts of co‐existing exotic and native legumes in a coastal dune ecosystem invaded by Acacia longifolia. Location An invaded coastal dune ecosystem in Portugal and reference bradyrhizobial strains from the Iberian Peninsula and other locations. Methods Symbiotic nitrogen‐fixing bacteria were isolated from root nodules of plants of the Australian invasive Acacia longifolia and the European natives Cytisus grandiflorus, Cytisus scoparius and Ulex europaeus. Total DNA of each isolate was amplified by polymerase chain reaction (PCR) with the primer BOX A1R. Subsequent PCR‐sequencing and phylogenetic analyses of the internal transcribed spacer region and the nifD and nodA genes were performed for all different strains. Results The four plant species analysed were nodulated by bacteria from three different Bradyrhizobium lineages, although most of the isolates belonged to the Bradyrhizobium japonicum lineage sensu lato. Ninety‐five per cent of the bradyrhizobia isolated from A. longifolia, C. grandiflorus and U. europaeus in the invaded ecosystem had nifD and nodA genes of Australian origin. Seven isolates obtained in this study define a new distinctive nifD group of Bradyrhizobium from western and Mediterranean Europe. Main conclusions These results reveal the introduction of exotic bacteria with the invasive plant species, their persistence in the new geographical area and the nodulation of native legumes by rhizobia containing exotic symbiotic genes. The disruption of native mutualisms and the mutual facilitation of the invasive spread of the introduced plant and bradyrhizobia could constitute the first report of an invasional meltdown documented for a plant–bacteria mutualism.     

Insights into the history of the legume‐betaproteobacterial symbiosis

The interaction between legumes and rhizobia has been well studied in the context of a mutualistic, nitrogen‐fixing symbiosis. The fitness of legumes, including important agricultural crops, is enhanced by the plants’ ability to develop symbiotic associations with certain soil bacteria that fix atmospheric nitrogen into a utilizable form, namely, ammonia, via a chemical reaction that only bacteria and archaea can perform. Of the bacteria, members of the alpha subclass of the protebacteria are the best‐known nitrogen‐fixing symbionts of legumes. Recently, members of the beta subclass of the proteobacteria that induce nitrogen‐fixing nodules on legume roots in a species‐specific manner have been identified. In this issue, Bontemps et al. reveal that not only are these newly identified rhizobia novel in shifting the paradigm of our understanding of legume symbiosis, but also, based on symbiotic gene phylogenies, have a history that is both ancient and stable. Expanding our understanding of novel plant growth promoting rhizobia will be a valuable resource for incorporating alternative strategies of nitrogen fixation for enhancing plant growth.     

Cyclic AMP in Rhizobia and Symbiotic Nodules

Cyclic adenosine 3',5'-monophosphate (cAMP) content of variouscultured rhizobia strains and tissues of legumes and non-leguminousplants was measured by enzyme immunoassays. Most rhizobia, culturedfor 44 to 165 h, contained cAMP ranging from 0.6 to 5 pmol mg^-1proteinexcept forAzorhizobium caulinodansORS571. The culture mediaalso contained varying amounts of cAMP depending on the strainof rhizobia.Azorhizobiumcells and their media contained no detectablecAMP. Nodules from most legumes and non-legumes had cAMP contentsranging from 2–70 pmol g^-1f.wt. However, nodules fromSesbaniarostrata,Crotalaria spectabilisandParasponia andersoniishowedundetectable cAMP levels, and those fromGlycine maxandVignaangularisoccasionally showed levels below the detection limit.The leaves of non-legumes mostly had cAMP levels below detectionlimit (approx. 1.0 pmol g^-1 f.wt), while the leaves ofa few legumes occasionally had detectable cAMP. The possiblerole of cAMP as a symbiotic signal is discussed. cAMP; legumes; modules; rhizobia; symbiosis     

Differential response of single and co-inoculation of <Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis> and <Emphasis Type="Italic">Mesorhizobium ciceri</Emphasis> for inducing water deficit stress tolerance in wheat

Limited soil water availability is a major threat to agricultural productivity because it inhibits plant growth and yields. Various strategies have been adopted to mitigate water deficit stress in plants; however, using extremophilic microbes with plant growth promoting traits could be an environmentally friendly and cost-effective approach to improve crop stress resilience. Rhizobia are well known for their symbiotic association with legumes, but they can also improve the fitness of non-legumes under stressed conditions. Thus, different rhizobial strains were isolated from nodules of two legumes (lentil and chickpea) and tested for osmoadaptation at four different polyethylene glycol (PEG-6000) levels, i.e., ? 0.05, ? 0.65, ? 1.57, and ? 2.17 MPa. Two stress-tolerant rhizobial strains, SRL5 and SRC8, were selected to evaluate their potential to induce tolerance against water deficits in wheat grown at four different percentages of field capacity (FC; 40, 60, 80, and 100%). Rhizobial inoculation improved physiological parameters and growth of wheat under water deficit; however, co-inoculation of selected rhizobia was better than sole application. Grain yield was most limited at the highest level of water deficit but sole inoculation with SRC8 and SRL5 improved yield by 24% and 19%, respectively. Combined inoculation increased grain yield by up to 48% compared to the uninoculated control. Thus, rhizobia from different legumes possess enormous potential for improving the resilience of cereals (non-legumes) to water deficit stress. Moreover, co-inoculation of rhizobia could be more beneficial than their sole application.     

Molecular diversity and phylogeny of indigenous <Emphasis Type="Italic">Rhizobium leguminosarum</Emphasis> strains associated with <Emphasis Type="Italic">Trifolium repens</Emphasis> plants in Romania

The symbiotic nitrogen fixing legumes play an essential role in sustainable agriculture. White clover (Trifolium repens L.) is one of the most valuable perennial legumes in pastures and meadows of temperate regions. Despite its great agriculture and economic importance, there is no detailed available information on phylogenetic assignation and characterization of rhizobia associated with native white clover plants in South-Eastern Europe. In the present work, the diversity of indigenous white clover rhizobia originating in 11 different natural ecosystems in North-Eastern Romania were assessed by a polyphasic approach. Initial grouping showed that, 73 rhizobial isolates, representing seven distinct phenons were distributed into 12 genotypes, indicating a wide phenotypic and genotypic diversity among the isolates. To clarify their phylogeny, 44 representative strains were used in sequence analysis of 16S rRNA gene and IGS fragments, three housekeeping genes (atpD, glnII and recA) and two symbiosis-related genes (nodA and nifH). Multilocus sequence analysis (MLSA) phylogeny based on concatenated housekeeping genes delineated the clover isolates into five putative genospecies. Despite their diverse chromosomal backgrounds, test strains shared highly similar symbiotic genes closely related to Rhizobium leguminosarum biovar trifolii. Phylogenies inferred from housekeeping genes were incongruent with those of symbiotic genes, probably due to occurrence of lateral transfer events among native strains. This is the first polyphasic taxonomic study to report on the MLSA-based phylogenetic diversity of indigenous rhizobia nodulating white clover plants grown in various soil types in South-Eastern Europe. Our results provide valuable taxonomic data on native clover rhizobia and may increase the pool of genetic material to be used as biofertilizers.     

Differential effectiveness of novel and old legume–rhizobia mutualisms: implications for invasion by exotic legumes

The degree of specialization in the legume-rhizobium mutualism and the variation in the response to different potential symbionts are crucial factors for understanding the process of invasion by exotic legumes and the consequences for the native resident plants and bacteria. The enhanced novel mutualism hypothesis predicts that exotic invasive legumes would take advantage of native rhizobia present in the invaded soils. However, recent studies have shown that exotic legumes might become invasive by using exotic introduced microsymbionts, and that they could be a source of exotic bacteria for native legumes. To unravel the role of novel and old symbioses in the progress of invasion, nodulation and symbiotic effectiveness were analyzed for exotic invasive plants and native co-occurring legumes in a Mediterranean coastal dune ecosystem. Although most of the studied species nodulated with bacteria from distant origins these novel mutualisms were less effective in terms of nodulation, nitrogenase activity and plant growth than the interactions of plants and bacteria from the same origin. The relative effect of exotic bradyrhizobia was strongly positive for exotic invasive legumes and detrimental for native shrubs. We conclude that (1) the studied invasive legumes do not rely on novel mutualisms but rather need the co-introduction of compatible symbionts, and (2) since exotic rhizobia colonize native legumes in invaded areas, the lack of effectiveness of these novel symbiosis demonstrated here suggests that invasion can disrupt native belowground mutualisms and reduce native legumes fitness.     

Effects of long‐term grazing management on sand dune vegetation of high conservation interest

Question: Can long‐term grazing management maintain and restore species‐rich sand dune plant communities within a sand dune site of high conservation interest? Location: Newborough Warren, North Wales, UK. Methods: Vegetation changes that occurred between 1987 and 2003, subsequent to grazing by domestic livestock being introduced to the site after decades with little or no stock grazing, were analysed using data collected from permanent monitoring quadrats over a 16‐year period. Results: At the plant community level, grazing brought about a shift from a tall‐grass dominated, species‐poor community to a more species‐rich community in the dry dunes, but did not change community type in dune slacks. However, at the species level, grazing enhanced the abundance of some desired perennial, annual and biennial species, graminoids and bryophytes in both habitat types. The increased frequency of positive indicator species for habitat condition suggests that grazing was beneficial for species of conservation interest. Ellenberg nitrogen (N) values decreased after grazing in dry habitats but showed no long‐term change independent of grazing, suggesting no increase in site fertility over the study period. Surprisingly, light (L) values also decreased in the dry dunes after grazing. Conclusions: Long‐term grazing management can play an important role for the conservation of dune communities and associated species. Because of its positive effects on species diversity, plant communities and habitat condition in sand dunes, livestock grazing is recommended for conservation management.     

Facilitation and sand burial affect plant survival during restoration of a tropical coastal sand dune degraded by tourist cars

Coastal sand dunes support various ecosystem services, including storm protection and tourism. Restoration programs are often critical to preserve this ecosystem due to its fragility and high degree of degradation. Dune restoration still suffers from a general lack of knowledge of the ecological processes controlling tropical dune communities. We investigated if facilitation can increase restoration success by assisting plant survival in a Brazilian coastal dune degraded by buggies at the Environmental Protection Area of Jenipabu, RN, Brazil. We performed two field experiments on dune crest sites degraded by buggies. The first experiment tested how the presence of established vegetation and coconut mesh, mimicking soil‐stabilizing effect of vegetation, facilitates seedling survival and establishment of the early successional dominant dune plant Canavalia maritima (Fabaceae). The second experiment tested if coconut mesh and initial irrigation would allow the establishment of C. maritima outside the vegetation, using both seeds and transplants. We found that the presence of established vegetation positively affected seedling survival. Application of mesh positively affected microclimatic conditions and slightly increased survival, but only for seeds. Initial irrigation only had a small effect on transplanted seedlings survival. Nevertheless, there was extreme seedling mortality in the experiment in particular from sand burial. We conclude that restoration of these dune crests is very difficult. Facilitation by vegetation can reduce plant mortality by sand burial and desiccation, but successful restoration is likely to require a major effort involving a very high number of seedlings or seeds.     

地中海沿岸沙丘微生境对幼苗出现时空格局的影响

实验样地设在地中海沿岸沙丘,选择了3个不同的微生境代表：(1)稳定沙丘上的开阔地片段,(2)稳定沙丘上的灌丛下区域,(3)不稳定沙丘的路径区域;从2001年11月至2002年4月的整个生长季节,每一个微生境出现的幼苗在4个日期被监测,并在每一个取样日把每一株幼苗鉴定、计数后,用剪刀把地上部分移去;研究调查了3种微生境幼苗出现的时空分布格局,并分析了雨量与幼苗出现数量的关系。结果发现：在地中海沿岸沙丘生态系统,幼苗出现在时间上具有明显的分布特征,大多数幼苗出现在第一观测期,整个生长季幼苗都不断出现,但幼苗出现的数目却逐渐下降;各功能群的幼苗占幼苗总数的比例分别为：1年生阔叶草47．4％,多年生阔叶草2．5％,豆科植物17,0％,菊科植物14．5％,1年生禾草为11．7％,多年生禾草为1．9％,十字花科植物3．7％,伞形科植物1,4％。在空间上,总幼苗密度、物种丰富度和物种多样性等显示出重要的微生境差异,开阔地区域具有最大的幼苗密度、物种丰富度和物种多样性;3个微生境的幼苗出现不是同步的,微生境影响种子萌发的时间分布格局,灌丛下种子萌发具有滞后现象;大多数功能群的幼苗密度分布基本上具有显著的微生境差异,主要物种的幼苗分布也具有显著的微生境差异。雨量和萌发的幼苗数量间未发现显著的关系。     

Four unnamed species of nonsymbiotic rhizobia isolated from the rhizosphere of Lotus corniculatus.

Previously, we found that genetically diverse rhizobia nodulating Lotus corniculatus at a field site devoid of naturalized rhizobia had symbiotic DNA regions identical to those of ICMP3153, the inoculant strain used at the site (J. T. Sullivan, H. N. Patrick, W. L. Lowther, D. B. Scott, and C. W. Ronson, Proc. Natl. Acad. Sci. USA 92:8985-8989, 1995). In this study, we characterized seven nonsymbiotic rhizobial isolates from the rhizosphere of L. corniculatus. These included two from plants at the field site sampled by Sullivan et al. and five from plants at a new field plot adjacent to that site. The isolates did not nodulate Lotus species or hybridize to symbiotic gene probes but did hybridize to genomic DNA probes from Rhizobium loti. Their genetic relationships with symbiotic isolates obtained from the same sites, with inoculant strain ICMP3153, and with R. loti NZP2213T were determined by three methods. Genetic distance estimates based on genomic DNA-DNA hybridization and multilocus enzyme electrophoresis were correlated but were not consistently reflected by 16S rRNA nucleotide sequence divergence. The nonsymbiotic isolates represented four genomic species that were related to R. loti; the diverse symbiotic isolates from the site belonged to one of these species. The inoculant strain ICMP3153 belonged to a fifth genomic species that was more closely related to Rhizobium huakuii. These results support the proposal that nonsymbiotic rhizobia persist in soils in the absence of legumes and acquire symbiotic genes from inoculant strains upon introduction of host legumes.     

Regional and local variation of spider assemblages (Araneae) from coastal grey dunes along the North Sea

Aim This study aims to determine the underlying causes of local and regional patterns of variation in community structure of spiders in coastal grey dunes, and especially whether ecological time constrains the species composition in young and isolated grey dune habitats. Location The study was conducted in coastal dunes from northern France (Boulonnais, Nord‐Pas‐de‐Calais), Belgium (Flemish coastal dunes) and the Netherlands [Amsterdam Water Supply (AWD) dunes and Dunes from the Provincial Water Company North‐Holland]. Methods Spiders were collected with pitfall traps in twenty‐eight grey dune patches in the four areas under investigation. Species composition and environmental parameters (vegetation structure, distance to the sea and the patch‐edge, eolic dynamics and lime richness) were determined. Assemblage composition was related to the regional and local environmental factors with the Primer software package to determine the assemblage‐determining parameters. Differences in species presence were analysed as a function of their habitat preference and distribution range. Results Differences in grey dune spider assemblage structure can mainly be attributed to differences in local sand dynamics and the region. Species from dynamic dunes are mainly present in grey dunes from Belgium and France, while species from non‐dunal xerothermic habitats (chalk grasslands and heathland) occur in both the Boulonnais and the north Holland dune region. These species are absent from geologically young or other xerotherm habitat isolated Flemish coastal dunes. Main conclusion The data show that regional variation in spider assemblage composition results from local landscape characteristics (dynamics in the dune area), the latitude and the connectivity to non‐dunal xerothermic habitats. The strong and moderate geological isolation of dune areas from the Flemish coast and the AWD dunes, respectively, results in the absence of (at least some) species that are primarily bound to heathland and/or chalk grassland. This indicates the importance of ecological time for the assemblage structure. The limited dispersal capacity of the heathland and/or chalk grassland species is probably the main reason for their absence.     

地中海沿岸沙丘种子大小对植物及其种子多度的影响

分析了地中海沿岸沙丘3种微生境(灌丛下、灌丛之间的开阔地、路径)以及整个沙丘生态系统的种子大小与土壤种子库中休眠种子的数量、土壤种子库中总种子的数量、地上植被中各个植物种的个体数量和幼苗数量、每种植物在小样方中的出现频率等方面之间的关系,也分析了种子尺寸(长、宽、高之和的平均值)与土壤种子的长久性、土壤种子库中休眠种子数量之间的关系;还分析了具有不同种子大小的植物在沙丘生态系统和各微生境的分布比率,验证了生活周期短的植物的种子在土壤中更长久和被干扰的微生境具有更多的休眠种子这种假说。结果发现,在地中海沿岸沙丘生态系统中,具有特别大的种子和特别小种子的植物种类都很少,不同植物种子的大小呈现近正态分布,但绝大多数植物的种子重量都不超过10 mg;微生境影响种子尺寸与种子长久性的关系,在灌丛下、开阔地区域等两个微生境以及整个的沙丘生态系统都呈现显著的正向关系(p<0 .0 5 ) ,而在路径这种关系不很明显;种子多度与植被物种出现频率呈现强烈的正相关(p<0 .0 5 ) ,没有发现种子大小与土壤种子库中休眠种子数量、种子库中总的种子数量、植被物种出现频率、植被的物种多度、幼苗植物多度等方面有显著的关系;具有中度大小种子(0 .1～10 mg)的植物在总的土壤种子库、休     

Sand Aggregation by Exopolysaccharide-Producing <Emphasis Type="Italic">Microbacterium arborescens––</Emphasis>AGSB

In the rhizosphere, exopolymers are also known to be useful to improve the moisture-holding capacity. The ability of the isolates from coastal sand dunes to produce exopolymers was determined. Among which the isolate, showing very high production of exopolysaccharide (EPS), Microbacterium arborescens––AGSB, a facultative alkalophile was further studied for exopolymer production. The isolate a gram-positive non-spore forming, slender rod, catalase positive, oxidase negative, showed growth in 12% sodium chloride. The culture was found to produce exopolymer which showed good aggregation of sand which has an important role in the stabilization of sand dunes. The exopolymer was further analysed. The cold isopropanol precipitation of dialysed supernatants grown in polypeptone yeast extract glucose broth produced partially soluble EPSs with glucose as the sole carbon source. Chemical analysis of the EPS revealed the presence of rhamnose, fucose, arabinose, mannose, galactose and glucose. On optimization of growth parameters (sucrose as carbon source and glycine as nitrogen source), the polymer was found to be a heteropolysaccharide containing mannose as the major component. It was interesting to note that the chemical composition of the exopolymers produced from both unoptimized and optimized culture conditions of Microbacterium arborescens––AGSB is different from those of other species from the same genera. This study shows that marine coastal environments such as coastal sand dunes, are a previously unexplored habitat for EPS-producing bacteria, and that these molecules might be involved in ecological roles protecting the cells against dessication especially in nutrient-limited environments such as the coastal sand dunes more so in the extreme conditions of pH. Such polysaccharides may help the bacteria to adhere to solid substrates and survive during the nutrient limitations.     

Structure, Pattern and Mechanisms of Formation of Seed Banks in Sand Dune Systems in Northeastern Inner Mongolia, China

A comparison of structure and pattern of the soil seed bank was made between active and stabilized sand dunes in northeastern Inner Mongolia, China. The objective of this paper was to determine the significance of seed bank in vegetation restoration of sand dunes. The results showed that (1) average seed density decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune; (2) horizontally, along the transect from interdune lowland to ecotone and to sand dune top, a ‘V’ shaped pattern was presented in the active dune system, and a reverse ‘V’ shaped pattern in the stabilized sand dune system; (3) vertically, the proportion (accounting for the total seeds) of seeds found in 0–20 mm soil profile decreased from stabilized sand dune to interdune lowland of stabilized sand dune, to interdune lowland of active sand dune, and to active sand dune. The same order was also found in 20–50 mm and 50–100 mm soil profiles; (4) the Sokal and Sneath similarity indices in the species-composition between soil seed bank and above-ground vegetation were ranked as: the stabilized sand dune (24%) > the interdune lowland of active sand dune (21%) > the interdune lowland of stabilized sand dune (18%) > the active sand dune (5%); and (5) vegetation restoration of active sand dunes depends on the dispersal of seeds from nearby plant communities on the interdune lowlands. Much effort must be made to preserve the lowlands, as lowlands are the most important seed reservoir in the active sand dune field.     

Arbuscular Mycorrhizae of Leymus arenarius on Coastal Sands and Reclamation Sites in Iceland and Response to Inoculation

The occurrence of arbuscular mycorrhizae fungi (AMF) was examined in natural and reclaimed sand dunes in Iceland. On the coastal sand‐plain of Myrdalssandur no spores of AMF were found on barren sand, and very few were found in 1‐ and 5‐year‐old reclamation sites of Leymus arenarius (lymegrass). A significantly higher number of AMF spores and root colonization were found in a 10‐year‐old reclamation site and in a natural old dune system of L. arenarius. AMF spores showed seasonal variation with higher occurrence in the fall than in the spring. On the volcanic island Surtsey, no AMF spores or root colonization were found on L. arenarius in 6‐ and 10‐year‐old dunes. However, AMF spores and root colonization were found in the 22‐year‐old Leymus dune. On Surtsey, a colonization pattern was found where AMF non‐dependent plants were the first colonizers followed by AMF facultative plants, then by AMF‐dependent plants. Today AMF facultative plants have the highest number of species but AMF non‐dependent plants have the largest population size. Three different AMF inocula were tested on L. arenarius; growth of seedlings was improved significantly by an indigenous AMF inoculum compared with commercial inocula. Inoculation of nursery grown seedlings of L. arenarius followed by transplantation into barren sand seeded with L. arenarius is recommended because this method will ensure establishment of the plant and enhance succession.     

Effects of salt spray and sand burial on Spinifex sericeus R. Br.

Abstract Spinifex sericeus, a common coastal sand dune grass, typically exhibits decreased vigour in the more stabilized section of the dunes when compared with the active foredune. These differences in vigour appear to be related to different environmental conditions across the dunes such as sand burial and salt spray deposition, both generally decreasing with distance inland. An experiment following the fate of foliar and root applications of ²²Na indicated that it may be taken up by the roots or the foliage and then translocated throughout the whole plant, and perhaps even extruded by the roots. Salt spray appeared to have a positive effect on the growth of S. sericeus when applied in conjunction with N and P but had no effect when N and P were not added. Adding acid-washed or non acid-washed foredune sand also resulted in a positive growth response. The results of these experiments indicate that the vigorous growth of S. sericeus on the dynamic sections of the foredunes is due to a stimulation of growth caused by sand deposition.     

High genetic and morphological diversity despite range contraction in the diploid Hieracium eriophorum (Asteraceae) endemic to the coastal sand dunes of south‐west France

Endemic plants inhabiting coastal sand dunes show augmented extinction risks due to the dynamic nature of dunes and strong human pressure on coastal areas. To investigate the survival strategies and threats to long‐term survival of such species, we combined genetic, morphological and biogeographical approaches, using the example of Hieracium eriophorum (Asteraceae) and its putative cryptic sister species H. prostratum, which are endemic to the longest coastal sand dune in Europe. An analysis of amplified fragment length polymorphism revealed high within‐population genetic variability, and slight isolation by distance was the only indication of genetic population structure. Thus, no signs of genetic threats to survival were found. Furthermore, genetic and morphometric data provided no evidence for the existence of two species. Therefore, we propose to synonymize H. prostratum with H. eriophorum and provide a nomenclatural overview with typification. Finally, an analysis of historical distribution records showed that, during the last 100 years, the species was lost from its range margins, where its habitat became fragmented. Taken together, our results suggest that one successful survival strategy of narrow endemics may be the achievement of large local population sizes on a small geographical scale, thus avoiding the genetic problems inherent to small and fragmented populations. Dune management policies should thus take care that the current tendencies to allow more erosion will not result in too severe fragmentation of the remaining continuous stretches of dune habitat. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 365–377.