首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
An increase of xenodiversity in plankton and benthos in the eastern Gulf of Finland was observed from 1998 to 2004. Nonindigenous species account for 4.8% of all species found and up to 96% of total biomass. Invasive benthic omnivores, the alien amphipods Gmelinoides fasciatus and Pontogammarus robustoides and the predaceous fish Perccottus glenii with their versatile diets strongly affect the community structure. Invasive sessile seston-feeders that directly (through grazing and water clearance) and indirectly (through recycling of nutrients) interact with other ecosystem components, are mainly represented by the zebra mussel Dreissena polymorpha, which affect the structure of benthic and planktonic communities as well as benthic-pelagic coupling. The invasive predatory cladocerans Cercopagis pengoi and Evadne anonyx and larvae of D. polymorpha are only temporary components in the zooplankton, which is limiting their overall effect. Alien benthic bioturbators, the polychaetes Marenzelleria neglecta and the oligochaete Tubificoides pseudogaster account for a high proportion of total abundance and biomass but their effects on native species need further research.  相似文献   

2.
Pitkänen  Sari 《Plant Ecology》2000,146(1):11-28
Diversity of vegetation in managed forests is studied. A classification based on forest stand structure, the abundances of vegetation species and variations in these abundances is developed and diversity indices are calculated for the classes to describe the diversity of the vegetation within the classes. The classes were formed using detrended correspondence analysis (DCA), global nonmetric multidimensional scaling (GNMDS) and TWINSPAN classification. Discriminant analysis was used to determine the environmental variables differentiating between the classes, and Duncan's multiple range test was used to examine the ability of the diversity measures to distinguish the classes. Beta diversity was estimated with Økland's method based on DCA ordination of the sample plots. The results point to fertility and the successional stage of the stand as the main factors affecting species diversity, in addition to which soil type, the number of tree species, crown cover, basal area and certain variables describing the management of the stand were relevant to the classification. The most distinct diversity indices were the reciprocal of Simpson, Pielou's J' and species richness, while the highest alpha diversity was found in young stands with a low crown cover on herb-rich or mesic forest sites. Beta diversity was quite high, its highest values of all for the whole data being recorded along the fertility gradient.  相似文献   

3.
The trophic status of the eastern Gulf of Finland, where the largest Baltic metropolis St. Petersburg sits at the mouth of the largest Baltic river Neva, is elevated but existing recommendations on water protection measures are controversial. In this study, the effects of nutrient load reductions on this ecosystem were estimated with the aid of a three-dimensional coupled hydrodynamic-biogeochemical model. As a reference, the contemporary seasonal dynamics were simulated with nutrient inputs corresponding to the recent estimates of point and riverine sources. In order to eliminate the effects of natural inter-annual variations, the computations were run under recurrent annual forcing for 3 years, until quasi steady-state seasonal dynamics were reached. Reasonable comparability of simulated concentrations and biogeochemical fluxes to available field estimates provides credibility to scenario simulations. These simulations show that substantial reductions of nutrient point sources in St. Petersburg would affect only the Neva Bay as the immediate receptor of treated sewage waters, where primary production could decrease by up to 20%. Eutrophication in the other parts of the Neva Estuary and in the entire eastern Gulf of Finland would change insignificantly owing to increased nutrient import from the offshore waters. Therefore, more significant changes can occur only via a reduction in nutrient pools in the open Gulf of Finland and the Baltic Proper, which would require a longer time. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark  相似文献   

4.
Model experiments on a possibility that pathogenic enterobacteria Salmonella enteritidis (Gartneri) can grow on decaying algal mats with prevalence of the filamentous algae Cladophora glomerata (L.) Kütz were carried out. Samples of algal mats have been collected in the eastern part of the Gulf of Finland in the Baltic Sea. A bacterial culture of Salmonella enteritidis was placed into tubes containing samples of mats. The intensive growth of salmonella was noted in alga samples collected in the freshwater zone (salinity 0.2–1.5‰); growth was practically absent in the samples of algae collected in a zone with salinity 2–3‰, while salmonella remained viable in the control tubes with water without algae. The growth of coliform enterobacteria initially inhabited in the algal mats was discovered in all experiments. Studies carried out in 2009 show that the thickness of the algal mats in the costal zones of the Gulf of Finland reached 20 cm and their biomass reached a few tons per 1 km2. These experiments showed that dead algal mats stimulate the growth of enterobacteria in the littoral zone of the Baltic Sea, especially in the freshwater part, and can promote the development of these pathogenic microorganisms.  相似文献   

5.
Lehtoranta  Jouni  Pitkänen  Heikki 《Hydrobiologia》2003,492(1-3):55-67
The relationships between P and components binding P were studied by analysing the concentrations of N, P, Fe, Mn, Ca and Al in sediments and pore water along the estuarine transect of the River Neva in August 1995. The high sediment organic matter concentration resulted in low surface redox potential and high pore-water o-P concentration, whereas the abundance of amphipods resulted in high surface redox potentials and low pore-water o-P concentration. However, despite the variation in sediment organic matter and the abundance of amphipods, very reduced conditions and slightly variable concentrations of Tot-P (0.7–1.1 mg g–1 DW) were observed in the 10–15 cm sediment depth along the estuarine gradient, indicating that the pools of mobile P were largely depleted within the depth of 0–15 cm. Multiple regression analysis demonstrated that organic matter and Tot-Fe concentration of the sediment were closely related to the variation in Tot-P concentration of the sediments (r 2 = 0.817, n=32). In addition, the high total Fe:P ratio suggested that there is enough Fe to bind P in sediments along the estuarine gradient. However, low Fediss concentrations in the pore water of reduced sediment (redox-potential <–50 mV) indicated efficient precipitation of FeS (FeS and FeS2), incapable to efficiently bind P. Consequently, the low Fediss:o-P ratio (< 1) recorded in pore water in late summer implied that Fe3+ oxides formed by diffusing Fediss in the oxic zone of the sediments were insufficient to bind the diffusing o-P completely. The measured high o-P concentrations in the near-bottom water are consistent with this conclusion. However, there was enough Fediss in pore water to form Fe3+ oxides to bind upwards diffusing P in the oxic sediment layer of the innermost Neva estuary and the areas bioturbated by abundant amphipods.  相似文献   

6.
7.
The field of genetic diversity in protists, particularly phytoplankton, is under expansion. However, little is known regarding variation in genetic diversity within populations over time. The aim of our study was to investigate intrapopulation genetic diversity and genetic differentiation in the freshwater bloom-forming microalga Gonyostomum semen (Raphidophyceae). The study covered a 2-year period including all phases of the bloom. Amplified fragment length polymorphism (AFLP) was used to determine the genetic structure and diversity of the population. Our results showed a significant differentiation between samples collected during the two blooms from consecutive years. Also, an increase of gene diversity and a loss of differentiation among sampling dates were observed over time within a single bloom. The latter observations may reflect the continuous germination of cysts from the sediment. The life cycle characteristics of G.?semen, particularly reproduction and recruitment, most likely explain a high proportion of the observed variation. This study highlights the importance of the life cycle for the intraspecific genetic diversity of microbial species, which alternates between sexual and asexual reproduction.  相似文献   

8.
Zhao QF  Wang G  Li QX  Ma SR  Cui Y  Grillo M 《Hereditas》2006,143(2006):33-40
Plants of the genus Kobresia are alpine grass species of high ecological and economic importance. Vegetative growth is the dominant means of reproduction for the Kobresia. Studies suggest that substantial vegetative growth can reduce genetic diversity and renders populations less able to buffer changing and extreme conditions. Kobresia are dominant species in the Qinghai-Tibet plateau in China where they face harsh conditions and frequent disturbance. The genetic diversity of five Kobresia species (K. humilis, K. royleana, K. kansuensis , K. tibetica and K. setchwanensis) from the Qinghai-Tibet plateau was assessed. The results reveal high genetic diversity at the population level for all of the species and there does not appear to be a relationship between altitude and genetic diversity. AMOVA analysis shows that most genetic variability resides among individuals within populations, whereas only a minor portion is found among populations. Of the five species, K. royleana and K. kansuensis have the highest levels of gene flow and the lowest genetic differentiation. While K. setchwanensis has the lowest gene flow and the greatest genetic differentiation. The level of gene flow between populations and the mating system play a critical role in the genetic structure of these Kobresia populations. Despite the predominance of vegetative growth enough sexual reproduction occurs to maintain the relatively high genetic diversity in Kobresia populations.  相似文献   

9.
The late summer mass occurrences of cyanobacteria in the Baltic Sea are among the largest in the world. These blooms are rarely monotypic and are often composed of a diverse assemblage of cyanobacteria. The toxicity of the blooms is attributed to Nodularia spumigena through the production of the hepatotoxic nodularin. However, the microcystin hepatotoxins have also been reported from the Baltic Sea on a number of occasions. Recent evidence links microcystin production in the Gulf of Finland directly to the genus Anabaena . Here we developed a denaturing gradient gel electrophoresis (DGGE) method based on the mcyE microcystin synthetase gene and ndaF nodularin synthetase gene that allows the culture-independent discrimination of microcystin- and nodularin-producing cyanobacteria directly from environmental samples. We PCR-amplified microcystin and nodularin synthetase genes from environmental samples taken from the Gulf of Finland and separated them on a denaturing gradient gel using optimized conditions. Sequence analyses demonstrate that uncultured microcystin-producing Anabaena strains are genetically more diverse than previously demonstrated from cultured strains. Furthermore, our data show that microcystin-producing Anabaena are widespread in the open Gulf of Finland. Non-parametric statistical analysis suggested that salinity plays an important role in defining the distribution of microcystin-producing Anabaena . Our results indicate that microcystin-producing blooms are a persistent phenomenon in the Gulf of Finland.  相似文献   

10.
11.
Mound‐building ants (Formica spp.), as key species, have large impacts on organisms and ecosystem functions in boreal Eurasian forests. The density, sizes and locations of ant mounds determine the magnitude and the spatial distribution of ant activities in forest ecosystems. Clear‐cutting can destroy wood ant colonies, and the species, abundance, dimensions and locations of ant mounds may change as forest stand structure changes with stand age. We compared ant species composition, ant mound numbers and dimensions, and the spatial distribution of mounds in Norway spruce [Picea abies (L.) Karst.] stands of different age (5, 30, 60 and 100 years) in eastern Finland. The mound density of Formica aquilonia Yarr. was greater in the two oldest stand age classes, while most mounds of Formica rufa L., Formica polyctena Först., Formica lugubris Zett., Formica exsecta Nyl. and Formica pressilabris Nyl. were found in the two youngest age classes. The mean volume, the volume per area and height/diameter ratio of F. aquilonia mounds increased with stand age. In the oldest stand age class, mounds were slightly smaller in well‐lit locations than in shade and near stand edges than further from the edges indicating that new mounds are established in well‐lit locations. Similarly, the longest slopes of the mounds faced south, indicating the importance of exposure to the sun. F. aquilonia mounds were concentrated near stand edges, and the spatial distribution of the mounds was aggregated in some stands. At the ecosystem level, the aggregation of ant mounds near stand edges may increase the edge productivity, as mounds concentrate resources to the edges and release nutrients after abandonment.  相似文献   

12.
13.
Tozer  M.G.  Bradstock  R.A. 《Plant Ecology》2003,164(2):213-223
Overstorey shrub species are known to influence the composition of theunderstorey in Southern Hemisphere heathlands. Overstorey densities aresusceptible to variations in fire frequency; thus, fire regimes may influenceoverstorey/understorey interactions and overall floristic composition. Wecompared patches of Banksia heath which had supported anoverstorey during a fire interval of about 30 y with patches wherethe overstorey was absent during the same period, and tested for differences inspecies composition as a function of overstorey presence. Floristic compositionvaried significantly between overstorey patches and open patches. Most specieswere less abundant in overstorey patches, however some were more abundant. Therelative abundance of species in relation to overstorey was unrelated to theirfire response, propagule longevity or propagule storage location. There wassignificantly less biomass in overstorey patches compared with open patches.Theeffect of the overstorey varied with soil moisture. In a dry area, the numberof species was lower in overstorey patches, with fewer herb and shrub speciespresent compared with open patches. Fewer species were recorded in a wetterarea, but overstorey had no effect on the number of species recorded. Reducedintensity of competition among understorey species in overstorey patches couldbe responsible for the higher abundance of some species in these patches. Wepostulate that full diversity will be maintained when the density of overstoreyshrubs fluctuates widely over a relatively short period of time. This is mostlikely when fire frequency is highly variable.  相似文献   

14.
Late summer cyanobacterial blooms in the Baltic Sea contain Anabaena sp. together with Nodularia spumigena and Aphanizomenon flos-aquae. Although Anabaena is common especially in the Gulf of Finland, very little is known about its genetic diversity. Here we undertook a molecular phylogenetic study of 68 Anabaena strains isolated from the brackish Gulf of Finland. We sequenced the 16S rRNA genes from 54 planktonic and 14 benthic Anabaena strains, and rbcL and rpoC1 genes from a subset of these strains. Phylogenetic trees showed that Anabaena strains, from both planktonic and benthic habitats, were genetically diverse. Although the Anabaena strains were morphologically diverse, in our study only one genetically valid species was found to exist in the plankton. Evolutionary distances between benthic Anabaena strains were greater than between planktonic strains, suggesting that benthic habitats allow for the maintenance of greater genetic diversity than planktonic habitats. A number of novel lineages containing only sequences obtained in this study were compiled in the phylogenetical analyses. Thus, it seemed that novel lineages of the genus Anabaena may be present in the Baltic Sea. Our results demonstrate that the Baltic Sea Anabaena strains show surprisingly high genetic diversity.  相似文献   

15.

Background and Aims

Intraspecific ploidy-level variation is an important aspect of a species'' genetic make-up, which may lend insight into its evolutionary history and future potential. The present study explores this phenomenon in a group of eastern Asian Cardamine species.

Methods

Plant material was sampled from 59 localities in Japan and Korea, which were used in karyological (chromosome counting) and flow cytometric analyses. The absolute nuclear DNA content (in pg) was measured using propidium iodide and the relative nuclear DNA content (in arbitrary units) was measured using 4,6-diamidino-2-phenylindole fluorochrome.

Key Results

Substantial cytotype diversity was found, with strikingly different distribution patterns between the species. Two cytotypes were found in C. torrentis sensu lato (4x and 8x, in C. valida and C. torrentis sensu stricto, respectively), which displays a north–south geographical pattern in Japan. Hypotheses regarding their origin and colonization history in the Japanese archipelago are discussed. In Korean C. amaraeiformis, only tetraploids were found, and these populations may in fact belong to C. valida. C. yezoensis was found to harbour as many as six cytotypes in Japan, ranging from hexa- to dodecaploids. Ploidy levels do not show any obvious geographical pattern; populations with mixed ploidy levels, containing two to four cytotypes, are frequently observed throughout the range. C. schinziana, an endemic of Hokkaido, has hexa- and octoploid populations. Previous chromosome records are also revised, showing that they are largely based on misidentified material or misinterpreted names.

Conclusions

Sampling of multiple populations and utilization of the efficient flow cytometric approach allowed the detection of large-scale variation in ploidy levels and genome size variation attributable to aneuploidy. These data will be essential in further phylogenetic and evolutionary studies.  相似文献   

16.
Associations between Trichinella species and host species in Finland   总被引:3,自引:0,他引:3  
Examination of 627 wild animals--raccoon dogs (Nyctereutes procyonoides), red foxes (Vulpes vulpes), European lynxes (Lynx lynx), brown bears (Ursus arctos), wolves (Canis lupus), and badgers (Meles meles)--revealed Trichinella spp. The prevalence varied according to geographical region of Finland (north; southwest, SW; and southeast, SE) and was the highest among lynxes (70%, SW). The risk of trichinellosis was higher in the SE (odds ratio, OR, 19.4) and SW regions (OR 14.3), as compared with the northern region (OR 1), with no difference between the former 2 regions. Foxes (OR 2.1) and lynxes (OR 1.9) had a higher risk than raccoon dogs (OR 1) of being infected. The distribution of different Trichinella species was evaluated in 87 wild and domestic mammals by multiplex polymerase chain reaction. Trichinella spiralis was detected more often in domestic and synanthropic animals than in sylvatic hosts. Trichinella nativa was detected only in wildlife. Trichinella pseudospiralis was found both in sylvatic and synanthropic hosts. Trichinella britovi was detected only in mixed infections with other Trichinella species. The raccoon dog was the sole host for all 4 Trichinella species and also carried the most intense infections.  相似文献   

17.
Sellner  K. G.  Olson  M. M.  Kononen  K. 《Hydrobiologia》1994,(1):249-254
Blooms of the cyanobacteria Nodularia spumigena and Aphanizomenon flos-aquae dominated the phytoplankton assemblages of the western Gulf of Finland and the eastern side of the northern Baltic Sea in late July–August, 1992. The bloom overlapped the peak seasonal contributions of the dominant mesozooplankton herbivores in the region, the copepods Acartia bifilosa and Eurytemora affinis and the cladoceran Bosmina longispina maritima. Using radio-labelling techniques; the copepods were offered one of the cyanobacteria, Nodularia, as well as the 10–54 µm fraction of the natural phytoplankton assemblage. In general, incorporation rates of the labelled phytoplankton into the copepods declined with increasing contributions of the cyanobacteria. For both copepods, incorporation was inversely related to total phytoplankton biomass, whether measured as chlorophyll, total cells or cyanobacteria biomass. The very low rates for Acartia (< 0.8 µl [copepod h]–1) indicated that this copepod was likely starving in the cyanobacteria bloom, consistent with the generally poor condition of the animal observed in the laboratory. The other major mesozooplanktor, B. longispina maritima, ingested substantially more cyanobacterial biomass than the two copepods, based on HPLC-identified cyanobacteria-specific pigment echinenone in the gut. Bloom carbon provided < 1% and < 4% of the daily rations for Acartia and Eurytemora, respectively. Total copepod demand in the cyanobacteria blooms was trivial, < 1% of bloom biomass consumed daily. These results suggest that copepod herbivory is relatively unimportant in dissipating summer cyanobacteria blooms in the Gulf of Finland.  相似文献   

18.
The eastern barred bandicoot, Perameles gunnii, has undergone a dramatic decline in distribution and abundance on the mainland of Australia during the twentieth century. In 1988 a captive breeding program was initiated to reduce the chance of extinction. With the extinction of the last wild mainland population in the early 1990s, reintroductions from captive-bred P. gunnii have met limited success, and currently only two extant populations persist in predator proof enclosures in the State of Victoria. With ~20 years of breeding, there are concerns that the genetic diversity within the breeding program has declined and may inhibit current and future success of the program. We have used ten nuclear microsatellite loci and sequencing of two partial mitochondrial genes (cytochrome oxidase I and ATPase 6) to determine genetic diversity within current Victorian P. gunnii. These diversity estimates are compared with historic samples from the captive breeding program dating back to 1995, historic samples from the last wild mainland population found at Hamilton in 1992 and contemporary Tasmanian wild populations. Results indicate that the captive P. gunnii population in the State of Victoria has lost significant genetic diversity through time. Genetic diversity is also reduced in populations at Hamilton Community Parklands and Mount Rothwell. Samples from the last wild population at Hamilton collected in 1992, along with samples from Tasmanian P. gunnii, had significantly greater genetic diversity than contemporary mainland populations. The results are discussed with reference to management options for maintaining genetic diversity within Victorian P. gunnii, including crossing Victorian and Tasmanian P. gunnii to increase genetic diversity, adaptability and evolutionary potential.  相似文献   

19.
Nutrient cycling within three Pinus sylvestris stands was studied in eastern Finland. The aim of the study was to determine annual fluxes and distribution of N, P, K, Ca, Mg, Zn, Fe, B, and Al in the research stands. Special emphasis was put on determining the importance of different fluxes, especially the internal cycle within the trees in satisfying the tree nutrient requirements for biomass production. The following nutrient fluxes were included, input; free precipitation and throughfall, output; percolation through soil profile, biological cycle; nutrient uptake from soil, retranslocation within trees, return to soil in litterfall, release by litter decomposition. The distribution of nutrients was determined in above- and belowground tree compartments, in ground and field vegetation, and in soil.The nitrogen use efficiencies were 181, 211 and 191 g of tree aboveground dry matter produced per g of N supplied by uptake and retranslocation in the sapling, pole stage and mature stands, respectively. Field vegetation was more efficient in nitrogen use than trees. Stand belowground/aboveground and fine root/coarse root biomass ratios decreased with tree age. With only slightly higher fine root biomass, almost three times more nitrogen had to be taken-up from soil for biomass production in the mature stand than in the sapling stand.The annual input-output balances of most nutrients were positive; throughfall contained more nutrients than was lost in mineral soil leachate. The sulphate flux contributed to the leaching of cations, especially magnesium, from soil in the mature stand.Retranslocation supplied 17–42% of the annual N, P and K requirements for tree aboveground biomass production. Precipitation and throughfall were important in transferring K and Mg, and also N in the sapling stand. Litterfall was an important pathway for N, Ca, Mg and micro nutrients, especially in the oldest stands.  相似文献   

20.
Macroalgal commercialization in the Orient   总被引:4,自引:0,他引:4  
Tseng  C. K  Fei  X. G. 《Hydrobiologia》1987,151(1):167-172
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号