Manipulation of cytosine methylation does not remove latitudinal clines in two invasive goldenrod species in Central Europe

Invasive species frequently differentiate phenotypically in novel environments within a few generations, often even with limited genetic variation. For the invasive plants Solidago canadensis and S. gigantea, we tested whether such differentiation might have occurred through heritable epigenetic changes in cytosine methylation. In a 2‐year common‐garden experiment, we grew plants from seeds collected along a latitudinal gradient in their non‐native Central European range to test for trait differentiation and whether differentiation disappeared when seeds were treated with the demethylation agent zebularine. Microsatellite markers revealed no population structure along the latitudinal gradient in S. canadensis, but three genetic clusters in S. gigantea. Solidago canadensis showed latitudinal clines in flowering phenology and growth. In S. gigantea, the number of clonal offspring decreased with latitude. Although zebularine had a significant effect on early growth, probably through effects on cytosine methylation, latitudinal clines remained (or even got stronger) in plants raised from seeds treated with zebularine. Thus, our experiment provides no evidence that epigenetic mechanisms by selective cytosine methylation contribute to the observed phenotypic differentiation in invasive goldenrods in Central Europe.     

草甘膦对入侵植物加拿大一枝黄花和伴生植物白茅光合特性的影响

入侵植物加拿大一枝黄花(Solidago canadensis)给许多地区带来了较大危害,目前常采用化学防除法进行防除,但除草剂防治入侵植物的同时难免会影响土著植物的生长。为探讨草甘膦对入侵植物与本地植物光合特性的影响,以加拿大一枝黄花及其伴生种白茅(Imperata cylindrica)为研究对象,采用盆栽控制试验方法,研究不同浓度草甘膦处理21后单种、混种加拿大一枝黄花和白茅的生长特征及光响应过程。结果表明:1)草甘膦显著抑制两种植物的生长。随处理浓度升高,加拿大一枝黄花的株高增长量不断减小、叶片枯萎率不断增加;白茅的分蘖死亡率、叶片枯萎率不断升高。白茅对草甘膦较敏感,0.6mL/L浓度下白茅先失绿,1.2mL/L下其分蘖死亡率、叶片枯萎率均超50%;1.8mL/L下加拿大一枝黄花叶片枯萎率超50%。施药后与单种相比,混种加拿大一枝黄花株高增长略快、叶片枯萎率略低,混种白茅分蘖死亡率及叶片枯萎率均较低,但单、混种之间差异不显著。种间关系显著影响白茅的分蘖数。2)随处理浓度递增,加拿大一枝黄花和白茅叶片净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)均不断降低,白茅下降更快。两个物种胞间CO_2浓度(C_i)的变化不同,随着浓度升高,单种加拿大一枝黄花C_i先下降而后上升,而混种时的C_i则不断下降;单、混种白茅C_i均上升。3)草甘膦显著影响加拿大一枝黄花和白茅最大净光合速率(P_(nmax))、光饱和点(LSP)和光补偿点(LCP);对两个物种暗呼吸速率(R_d)的影响不显著,对加拿大一枝黄花表观量子效率(AQY)的影响同样不显著,但显著影响白茅AQY。种植方式显著影响两个物种P_(nmax)、LSP以及白茅R_d和AQY。0.6mL/L草甘膦对混种加拿大一枝黄花和白茅P_(nmax)的影响要大于对单种植株的影响,随处理浓度上升,对不同种植方式下两种植物P_(nmax)的影响趋近。与本地种白茅相比,入侵植物加拿大一枝黄花具有更高的光合速率和生长速率;草甘膦显著降低两个物种的生长和光合作用,白茅对草甘膦处理更敏感。     

Increased survival of Dalbulus maidis, a specialist on maize, on non-host plants infected with mollicute plant pathogens

The leafhopper Dalbulus maidis DeLong & Wolcott survived significantly longer on aster, Callistephus chinensis Nees, infected with any one of 3 strains of aster yellows (AY) mycoplasma-like organism (MLO) than on healthy asters. After 7 or more days on AY-diseased aster, females were conditioned to survive longer on healthy asters than were leafhoppers of the same age previously exposed only to maize. Females were also conditioned to survive longer on healthy aster by prior exposure to AY-MLO-infected celery (Apium graveolens L.). Males were not so conditioned. Leafhoppers injected with infectious extracts of AY-MLO dit not live longer on aster nor transmit the AY-MLO to aster. Conditioning on AY-diseased aster did not cause D. maidis to transmit AY-MLO and did not interfere with the transmission to maize of the mollicute (Spiroplasma kunkelii Whitcomb et al.) that causes corn stunt disease. Spiroplasma citri Saglio et al. infection of aster but not of turnip (Brassica rapa L.), Plantago major L. or periwinkle (Catharanthus roseus (L.)), improved the longevity of D. maidis on these plants and conditioned leafhoppers for enhanced subsequent survival on healthy asters.

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Résumé La cicadelle du maïs, D. maidis à survécu significativement plus longtemps sur aster (Callistephus chinensis Nees) contaminé par l'une des trois souches de l'agent mycoplasmique (MLO) de la jaunisse de l'aster (AY), que sur des asters sains. Après 7 jours ou plus sur des asters AY-MLO, les femelles (et non les mâles) étaient conditionnées de telle sorte qu'elles survivaient plus longtemps sur asters sains que des femelles du même âge précédemment sur maïs. Sur des céleris (Apium graveolens) atteints de AY, D. maidis a survécu plus longtemps que sur céleri sain, mais moins que sur aster AY. Des extraits, contaminés par AY injectés à D. maidis n'ont pas augmenté sa longévité sur aster, ni provoqué la transmission de AY-MLO. Le conditionnement sur aster AY n'a pas entrainé la transmission de AY-MLO par D. maidis, et n'a pas interferé avec son aptitude à transmettre l'agent du nanisme du maïs, Spiroplasma kunkelii. S. citri a aussi conditionné D. maidis sur aster, mais a été sans effet sur navet (Brassica rapa), sur plantain (Plantago major) et sur pervenche (Vinca).

     

Patch colonization by Trirhabda canadensis (Coleoptera: Chrysomelidae): effects of plant species composition and wind

Summary The goldenrod leaf beetle, Trirhabda canadensis, is known to respond to odors of host and non-host species in the laboratory. Here we report movements of T. canadensis in the field in response to volatile odors from monocultures and polycultures of host plants. Overall, beetles preferentially colonized plots with a higher density of host plants and lower diversity of allelochemicals, but under some wind conditions there were marked exceptions. At high windspeeds, they colonized whichever plot(s) was upwind. At low windspeeds, beetles colonized preferred plots even when they were not upwind. The data suggest that odor dispersion varies in a complex way with windspeed: at low windspeeds beetles received information from a wide are of vegetation and made choices while at high windspeeds information was available only from upwind plot(s).     

Impact of tree species on nutrient and light availability: evidence from a permanent plot study of old-field succession

This paper compares vegetation composition, light availability, carbon and nutrient pools and Ellenberg indicator values among four old-field successional permanent plots that have received an initial treatment (ploughing, herbicide or sterilisation) prior to being left undisturbed in 1969, a second set of six plots received additional treatments (continued ploughing or mulching until 1982). On all plots species rich pioneer forests developed. Vegetation still varies among plots with different initial treatments: Sterilised plots can be distinguished from the others by dominance of Betula pendula, ploughed plots by Fraxinus excelsior, whereas herbicide-treated plots are intermediate with proportions of both species. By affecting light availability at the ground, tree species in turn influences ground vegetation and soil properties. Light availability turned out to be the dominant factor determining the composition of the vegetation in old-field succession.     

Ultrastructural basis of mitosis in the fungusNectria haematococca (sexual stage ofFusarium solani)

Summary Microtubules (MTs) in the mitotic asters of the fungusNectria haematococca (teleomorph ofFusarium solani f. sp.pisi) pull on the spindle pole bodies (SPBs) during anaphase. To elucidate the structural basis of astral forces, we conducted an ultrastructural study using primarily freeze-substitution, three-dimensional reconstruction, and computerized numerical data acquisition and analysis. The asters were composed of numerous (68–171), mostly short (<0.5 m) MTs and varied widely in total MT length (34–83 m). Both the number and total length of MTs varied up to twofold or more among asters, even between the two asters of the same mitotic apparatus (MA). Surprisingly, less than one half (38%) of the MTs in each aster were attached to the SPB. Both the number and total length of these polar MTs varied up to twofold between the two asters of the same MA. Some asters included MTs oriented back toward the opposite SPB, whereas others did not, and the number and total length of such MTs varied among asters. These results are best interpreted by assuming that astral MTs inN. haematococca have a rapid rate of turnover and exhibit dynamic instability. Any of these parameters of astral architecture could vary during mitosis and thereby give rise to the oscillations of the mitotic apparatus that occur during anaphase B by generating unequal and fluctuating forces in the two sister asters. Astral MTs were arranged asymmetrically around the astral axis, and this asymmetry could produce the lateral movements of the SPB that occur during anaphase B. An apparently extensive system of 10nm filaments occurred in these cells, and some astral MTs were associated either terminally (at the plasma membrane) or laterally with these filaments. Such associations could be involved in the development and maintenance of astral forces.Abbreviations fMT free microtubule - MA mitotic apparatus - MT microtubule - pMT polar microtubule - SPB spindle pole body     

Ecological divergence among five co-occurring species of old-field goldenrods

Approximately 130 species of goldenrods are native to North America and many occur sympatrically. Such cooccurrence among closely related species raises the question of whether differences among the species in smallscale distribution and growth forms facilitate their co-occurrence. We investigated five goldenrods that frequently co-occur within their native ranges in Pennsylvania USA old fields. We measured goldenrod abundances, soil textures, nutrients, pH, and moisture within 30 old fields, and determined biomass allocation and flower and seed traits for each goldenrod species at a common site. Ordination revealed that Solidago altissima and S. gigantea were associated with fields having circum-neutral soils, whereas Euthamia graminifolia and S. rugosa achieved their highest abundances on acidic soils. Soil clay content and moisture may be associated with a further separation of species as the abundance of S. altissima tended to be higher on well-drained soils while S. gigantea had a tendency to attain its highest abundances on moist soils that had relatively stable moisture levels over time. Euthamia was more likely to be abundant on clay-rich soils while S. rugosa was often associated with soils containing little clay. Solidago juncea tended to associate with droughty soils that underwent marked soil-moisture changes over time. The latter goldenrod had the greatest absolute and relative root mass, the least absolute and relative leaf mass, highest seed-reproductive allocation, and heaviest achenes. In contrast, S. gigantea and Euthamia, which were often associated with more mesic and stable soil moisture conditions, allocated the least to roots and relatively high amounts of mass to leaves. Solidago gigantea, S. altissima, and Euthamia are invasive species across Europe. The species with the highest colonization rate across Europe, S. gigantea, allocated the most to reproduction in our study, while S. altissima, with the second highest colonization rate, was highly clonal producing the most rhizome mass. Life-history trait variation among goldenrods appears to be linked to differences in small-scale distributions and rates of colonization.     

How many heteropteran species can live on alien goldenrods Solidago canadensis and S. gigantea in Europe?

During the vegetation periods of 2001–2003 Heteroptera associated with the invasive alien tall goldenrods Solidago canadensis and S. gigantea were studied in seven model habitats in the north-eastern part of the Czech Republic. Heteropterans associated with adjacent growths were also studied in 2002–2003. A set of 3,042 specimens of 127 samples was analyzed with the aim of estimating average species richness, abundance and trophic structure of the heteropteran assemblages of the studied plant stand. On alien Solidago, 68 heteropteran species were recorded and 71 species were collected in the stands adjacent to the tall goldenrods with 48 shared species. Despite the nearly indentical species richness and similar abundances in Solidago and adjacent stands, there are differences in the trophic structure. The majority of the shared species and species found on Solidago canadensis only are polyphagous contrary to the majority of stenophagous species found on Solidago free stands only. Only a small proportion of heteropteran species that were recorded on alien Solidago stands are specialized to Asteraceae and their abundance was mostly low. Only the lygaeid Nysius senecionis, an Asteraceae specialist, occured in masses on S. canadensis in sunny and warm habitats. Similarly, predatory Orius minutus and O. niger reached high abundance values in Solidago stands compared to adjacent stands.     

Lupinus species differ in their requirements for iron

The effect of iron supply on the growth and nodulation ofLupinus angustifolius L. (Gungurru),Lupinus luteus L. (R-1171) andLupinus pilosus Murr. (P20957) was studied in acid solutions. Plants of the three species were grown together in the same solution and inoculated withBradyrhizobium (Lupinus) WU 425. Plants were then grown with or without applied NH₄NO₃. The lupin species differed greatly in their sensitivity to low iron concentrations in solution withL. pilosus being most tolerant andL. luteus most sensitive.L. pilosus had the highest iron concentration in tissues and had a higher ratio of iron concentration in the youngest fully expanded leaf blades (YEB) to that in roots than the other two species.L. luteus had higher iron concentrations in roots but lower iron concentration in YEB and shoots than didL. angustifolius. The requirements of internal iron for the maximal chlorophyll synthesis in YEB were 65 μg g^-1 forL. angustifolius andL. luteus, and 52 μg g^-1 forL. pilosus. In contrast to effects on growth, the three species had similar external iron requirements for nodule formation in roots and for maximal nitrogen concentrations in shoots. The results indicate that iron tolerant lupin species require lower internal and external iron supply and have a greater ability than sensitive species to translocate iron from roots to shoots.     

Evolution of an invasive phenotype: shift to belowground dominance and enhanced competitive ability in the introduced range

In response to novel selection pressures in an introduced range, non-native species may evolve more competitive phenotypes unique from those of their native range. We examined the existence of an invasive phenotype in the herbaceous perennial Artemisia vulgaris, a frequent invader of the Northeast and Mid-Atlantic US. Populations from both the native (European) and the introduced (North American) ranges were grown in intra-specific competition (same population), inter-specific competition with the native perennial herb Solidago canadensis, and alone in a common garden to quantify shifts in resource allocation and neighbor effects on performance and competitive ability. Without competition, introduced A. vulgaris populations were much shorter than native populations, but germinated earlier, produced more ramets, more belowground and total biomass, and maintained higher root-to-shoot ratios. Under inter- and intra-specific competitions, introduced A. vulgaris populations were shorter, but produced more ramets, belowground, and total biomass than native populations. S. canadensis belowground and total biomass were more highly suppressed by introduced than native A. vulgaris. Our data suggest that since the introduction to North America, A. vulgaris has evolved a more competitive invasive phenotype characterized by many short ramets with more extensive root/rhizome networks. This rapid evolutionary shift likely benefits A. vulgaris in its introduced range by allowing establishment and subsequent dominance in dense stands of existing vegetation.     

Top-down effects of insect herbivores during early succession: influence on biomass and plant dominance

We tested the hypothesis that phytophagous insects would have a strong top-down effect on early successional plant communities and would thus alter the course of succession. To test this hypothesis, we suppressed above-ground insects at regular intervals with a broad-spectrum insecticide through the first 3 years of old-field succession at three widely scattered locations in central New York State. Insect herbivory substantially reduced total plant biomass to a similar degree at all three sites by reducing the abundance of meadow goldenrod, Solidago altissima. As a result, Euthamia graminifolia dominated control plots whereas S. altissima dominated insecticide-treated plots by the third year of succession. S. altissima is the dominant old-field herbaceous species in this region but typically requires at least 5 years to become dominant. Past explanations for this delay have implicated colonization limitation whereas our data demonstrate that insect herbivory is a likely alternative explanation. A widespread, highly polyphagous insect, the xylem-tapping spittlebug, Philaenus spumarius, appeared to be the herbivore responsible for the reduction in standing crop biomass at all three sites. Insect herbivory typically caused little direct leaf tissue loss for the ten plant species we examined, including S. altissima. Consequently, the amount of leaf area removed was not a reliable indicator of the influence of insect herbivory on standing crop biomass or on early succession. Overall, we found a strong top-down effect of insect herbivores on biomass at several sites, so our results may be broadly applicable. These findings run counter to generalizations that top-down effects of herbivores, particularly insects, are weak in terrestrial systems. These generalizations may not apply to insects, such as spittlebugs, that can potentially mount an effective defense (i.e., spittle) against predators and subsequently reach relatively high abundance on common plant species. Our results suggest that insect herbivory may play an important but often overlooked role during early old-field succession. Received: 26 December 1998 / Accepted: 3 April 1999     

Characterization of biocontrol traits in the entomopathogenic nematode Heterorhabditis georgiana (Kesha strain), and phylogenetic analysis of the nematode’s symbiotic bacteria

Our objective was to estimate the biocontrol potential of the recently discovered entomopathogenic nematode species Heterorhabditis georgiana (Kesha strain). Additionally, we conducted a phylogenetic characterization of the nematode’s symbiotic bacterium. In laboratory experiments, we compared H. georgiana to other entomopathogenic nematodes for virulence, environmental tolerance (to heat, desiccation, and cold), and host seeking ability. Virulence assays targeted Acheta domesticus, Agrotis ipsilon, Diaprepes abbreviatus, Musca domestica, Plodia interpunctella, Solenopsis invicta, and Tenebrio molitor. Each assay included H. georgiana and five or six of the following species: Heterorhabditis floridensis, Heterorhabditis indica, Heterorhabditis mexicana, Steinernema carpocapsae, Steinernema feltiae, Steinernema rarum, and Steinernema riobrave. Environmental tolerance assays included Heterorhabditis bacteriophora, H. georgiana, H. indica, S. carpocapsae, S. feltiae, and S. riobrave (except cold tolerance did not include S. carpocapsae or S. riobrave). Host seeking ability was assessed in H. bacteriophora, H. georgiana, S. carpocapsae, and Steinernema glaseri, all of which showed positive orientation to the host with S. glaseri having greater movement toward the host than S. carpocapsae (and the heterorhabditids being intermediate). Temperature range data (tested at 10, 13, 17, 25, 30 and 35 °C) indicated that H. georgiana can infect Galleria mellonella between 13 and 35 °C (with higher infection at 17–30 °C), and could reproduce between 17 and 30 °C (with higher nematode yields at 25 °C). Compared with other nematode species, H. georgiana expressed low or intermediate capabilities in all virulence and environmental tolerance assays indicating a relatively low biocontrol potential. Some novel observations resulted from comparisons among other species tested. In virulence assays, H. indica caused the highest mortality in P. interpunctella followed by S. riobrave; S. carpocapsae caused the highest mortality in A. domesticus followed by H. indica; and S. riobrave was the most virulent nematode to S. invicta. In cold tolerance, S. feltiae exhibited superior ability to cause mortality in G. mellonella (100%) at 10 °C, yet H. bacteriophora and H. georgiana exhibited the ability to produce attenuated infections at 10 °C, i.e., the infections resumed and produced mortality at 25 °C. In contrast, H. indica did not show an ability to cause attenuated infections. Based on the phylogenetic analysis, the bacterium associated with H. georgiana was identified as Photorhabdus luminescens akhurstii.     

加拿大一枝黄花提取物的抗氧化活性研究

为进一步开发和利用加拿大一枝黄花(Solidago canadensis),该研究采用氯化铝显色法和福林酚法测定加拿大一枝黄花乙醇提取物及其不同极性萃取物中的总黄酮和总酚的含量;以抗坏血酸(Vitamin C,Vc)和二丁基羟基甲苯(BHT)为阳性对照,应用2,2-联氮-二(3-乙基-苯并噻唑-6-磺酸)二铵盐(ABTS)、1,1-二苯基苦基苯肼(DPPH)自由基清除体系、铁离子还原能力(FRAP)法和抗氧化能力指数(ORAC)法研究其体外抗氧化活性。结果表明:乙酸乙酯萃取物中的总黄酮(202.45 mg·g~(-1))和总酚(485.94 mg·g~(-1))含量最高,且其抗氧化活性最强,并强于阳性对照Vc(P0.05)。因而,加拿大一枝黄花乙酸乙酯萃取物将有可能成为一种潜在的天然高效抗氧化剂,具有广泛的应用前景。     

Reproductive biology in an invasive plant Solidago canadensis

Solidago canadensis, a perennial Compositae plant originating from North America, was introduced into China as a horticultural plant in 1935. Under natural conditions, S. canadensis allocates large amounts of energy to sexual reproduction and produces many seeds, which reflects an r-strategy with high seed number and small seed size. In addition, naturalized populations have a great capacity to grow clonally with underground stems. S. canadensis has become an invasive weed in eastern China, and has caused serious damages to agricultural production and ecosystems in several provinces in China. In order to understand the reproductive characteristics of S. canadensis and effectively control its spread, we examined soil conditions, seed characteristics, seed germination and the capacity for asexual reproduction in different plant parts. We investigated the population dispersion of S. canadensis in fixed sites for three years, and analyzed the seasonal dynamics of the morphological parameters of the underground parts and the caloric values of different organs of S. canadensis. We also compared differences in the root systems of S. canadensis and composite exotic weeds. The following results were obtained:

Food plant choices of two goldenrod beetles: Relation to plant quality

Summary The leaf beetles Trirhabda borealis and T. virgata are specialist herbivores of meadow goldenrods, Solidago spp., in central New York. Upon emergence, both larvae and adults must actively search for food plants, and must choose among the five goldenrod species (S. canadensis, S. gigantea, S. graminifolia, S. juncea and S. rugosa) that co-occur in old fields. The relationship between Trihabda foraging decisions and plant quality was examined by comparing food preferences in the field with the performance of beetles caged on each host. Trirhabda adults were highly selective in their use of food plants. Adults of T. borealis preferred a single host, S. canadensis, while T. virgata adults were most common on S. canadensis and S. gigantea. These preferences were not strictly related to variation in plant quality. In the laboratory, T. borealis performed equally well on four goldenrods (but completely failed to reproduce when fed S. graminifolia), and T. virgata performed equally well on all five hosts.Larval feeding preferences in each beetle species were broader, and were more in accord with subtle variation in plant quality. Newly-hatched T. borealis larvae readily colonized four hosts and rejected only S. graminifolia, which conferred the lowest survivorship and the slowest growth. Larvae of T. virgata accepted each host, even though growth rates were somewhat slower on S. graminifolia and S. juncea.Ontogenetic differences in host preference and host tolerance may have evolved because of the different host-finding abilities of each beetle stage. During host search, the sluggish, newly-emerged larvae may be more food-limited and accept even marginally inferior food plants. The relatively mobile adults are more discriminating and use a subset of suitable hosts. The intermingled dispersion of Solidago species in old fields results in frequent larval colonization of hosts seldom used by adults. In diverse plant communities, ultimate patterns of food plant choice can be a complex function of at least three factors: intrinisic plant quality, local plant dispersion, and the host-search abilities of the insect forager.     

A fast and simple genetic survey reveals the spread of poplar hybrids at a natural Elbe river site

It is known that various poplar species and cultivated poplar hybrids have the potential to interbreed and produce fertile offspring. Conservation strategies for the genetic resources of the endangered Eurasian black poplar (Populus nigra L.) thus rely on a monitoring which enables the identification and verification of the pure species status. At the same time, the risk of hybrid dispersal and introgressive gene flow has to be estimated. In the present study a combination of two molecular markers, one from chloroplast DNA and the other from nuclear DNA, was applied to evaluate a large P. nigra population on the Elbe River. Hybrid clones of P. × canadensis are scattered within this population and also occur as plantations in the surrounding landscape. By means of the DNA markers the taxonomic status of 208 adult trees in the population and 140 young poplars along the riverbank was monitored. From the analysed young poplars, almost 20 percent were found to exhibit at least one of the two P. deltoides or P. × canadensis diagnostic alleles or genotypes, respectively. Possible vegetative spreads of F1 hybrids and precedent mating scenarios are discussed. Most interestingly we found clear evidence for a small number of backcross hybrids where P.  × canadensis acted as pollen donor. This case had long been debated and thought to be less probable, so far.     

南京市加拿大一枝黄花入侵地群落的物种组成与多样性特征研究(附表)

为探究外来植物加拿大一枝黄花(Solidago canadensis)入侵与南京市本土植物多样性的关系,该文采用踏查及样方调查对其入侵地群落的物种组成与多样性进行研究。结果表明:(1)入侵地群落中共有维管植物200种(含种下单元),隶属于62科156属,其中被子植物195种,裸子植物1种,蕨类植物4种; 数量最多的是菊科(Asteraceae)和禾本科(Poaceae)植物,分别有25种和24种; 从生活型来看,草本植物占多数,有133种,占所有种的66.50%; 此外,群落内尚有其他外来植物29种。群落中重要值最大的是加拿大一枝黄花,为40.00%; 其次是救荒野豌豆(Vicia sativa),为7.00%。(2)从植物区系看,非入侵地中植物科的区系分布型共4个,而入侵地植物科的区系类型仅有3个,其中泛热带分布、世界分布和北温带分布为两者均有,东亚和北美间断分布型仅在非入侵地中存在。非入侵地植物科的区系以世界分布型为主,有13科,占该类型群落中所有科的39.39%; 入侵地则以泛热带分布型为主,有16科,占总科数的45.71%。非入侵地中植物属的区系分布型有10个,而入侵地有12个,两者区系成分相近,旧世界热带型和热带亚洲至热带大洋洲分布型仅在入侵地中出现。北温带分布型和世界分布型同为两者中最主要成分。入侵地及非入侵地群落属的区系R/T值分别为0.58和0.38,种系分化度分别为3.29和3.11。(3)重度入侵群落的Margalef指数(E)与非入侵及轻度入侵群落相比,显著降低; 此外,重度入侵群落的Simpson指数(D)、Shannon-Weiner(H'')指数和Pielou指数(J)均显著低于非入侵、轻度入侵、中度入侵群落。(4)不同生境之间加拿大一枝黄花群落的E、D、H''和J均无显著性差异。该研究可为南京地区的加拿大一枝黄花入侵地的治理防控和生态恢复,以及进一步的科学研究提供强有力的理论支撑。     

Patterns in the distribution of myctophid fish in the northern Scotia Sea ecosystem

The mesopelagic fish community of the northern Scotia Sea was investigated during the austral autumn using multi-frequency acoustics, opening and closing nets and pelagic trawls fished from the surface to 1,000 m. The Family Myctophidae (15 species in 5 genera) dominated the ichthyofauna, with larval notothenids caught over the South Georgia shelf and bathylagids and stomiids abundant in deeper hauls. The biomass of myctophids was estimated to be 2.93 g wet weight 1,000 m⁻³, with Electrona carlsbergi, E. antarctica, Protomyctophum bolini, P. choriodon, Gymnoscopelus braueri, G. fraseri, G. nicholsi and Krefftichthys anderssoni, being the most abundant species. Analysis of community structure indicated a high level of depth stratification within the myctophids, with evidence of diurnal vertical migration in some, but not all, species. Length-frequencies of G. braueri, G. nicholsi, E. antarctica and K. anderssoni were multimodal, suggesting that all life stages may be present in the northern Scotia Sea. In contrast, P. choriodon, P. bolini, G. fraseri and E. carlsbergi had unimodal distributions despite having multi-year lifecycles, indicating that they probably migrate into the region from warmer areas to the north.     

Can Gas-Exchange Characteristics help Explain the Invasive Success of Lythrum salicaria?

Since its introduction to North America, Lythrum salicaria (L.) (purple loosestrife) has become invasive in marshy and riparian habitats. We compared gas-exchange responses to external CO₂ partial pressure and light, as well as related leaf structural and biochemical characteristics, of L. salicaria with those of co-occurring native Asclepias syriaca (common milkweed) and Solidago graminifolia (lance-leaved goldenrod) along a pond bank in the Black Rock Forest, Cornwall, New York, USA to examine if the invasive success of L. salicaria may be influenced by robust leaf gas-exchange characteristics, including relatively high rates of photosynthesis and low rates of respiration, compared with those of less successful co-occurring native plant species. Neither the mean rate of net photosynthesis measured at ambient CO₂ and saturating photon flux density (A) nor the mean dark respiration rate (R_D) differed significantly between L. salicaria and either of the native species, while both the mean maximum rate of photosynthesis at saturating CO₂ concentration and photon flux density (A _max) and the mean rate of respiration measured in light (R_L) were significantly higher in L. salicaria than A. syriaca, but no different between L. salicaria and S. graminifolia. Likewise, photosynthetic nitrogen-use efficiency was greater in L. salicaria than A. syriaca only, while photosynthetic water-use efficiency was significantly less in both L. salicaria and S. graminifolia than in A. syriaca. Despite limited interspecific differences in leaf photosynthesis, respiration, and resource-use efficiency, particularly between L. salicaria and S. graminifolia, we found that L. salicaria assimilated 208% more carbon per unit of energy invested in leaf biomass than either of the co-occurring native species, suggesting that increased photosynthetic energy-use efficiency may influence its observed invasive success. This revised version was published online in July 2006 with corrections to the Cover Date.