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1.
79 taxa of desmids belongig to 17 genera were observed in 17 samples collected from several parts in Basrah district, South Iraq. 3 genera viz. Actinotaenium, Docidium and Spondylosum, and 41 taxa are new records for Iraqi waters. Distribution of taxa in the area studied as well as in the whole country (when available) are given. Some slight morphological variations in desmids were observed due to the alkaline nature of water.  相似文献   

2.
The fate of 15NH inf4 sup+ and 15NOinf3 was followed in control and PO inf4 sup3− enriched 1570 l mesocosms filled with epilimnetic water from an oligotrophic Rocky Mountain lake. Volumetric incorporation of 15NH inf4 sup+ and 15NO inf3 sup− into phytoplankton and bacterioplankton (particulates between 280 and 0.7 μm), and crustacean zooplankton > 80 μm was enhanced by PO inf4 sup3− , but no increase in biomass specific rates of uptake by phytoplankton and bacteria occurred for either form of 15N. Dilution of both 15NH inf4 sup+ and 15NO inf3 sup− by 14NH inf4 sup+ and 14NO inf3 sup− , respectively, was evident indicating regeneration of these nutrients, but regeneration rates were not effected by PO inf4 sup3− enrichment. The results illustrate the strong trophic coupling between N dynamics and PO inf4 sup3− enrichment in this system.  相似文献   

3.
Summary

From some 50 samples collected in many parts of Scotland in 1996, 15 sites have been selected as containing rare or at least unusual desmids. The sites are listed and the desmids, some new records for the British Isles, are illustrated.  相似文献   

4.
Summary

A detailed survey of the desmid flora of the area covered by the parish of Assynt, West Sutherland is currently being made by the author. During the course of the study so far, a number of either rare or hitherto unrecorded desmids for the British Isles has been found. Two such desmids are now described.  相似文献   

5.
Suspended and benthic algal communities from a mildly acidic, third-order Rhode Island stream were examined to determine the seasonal distribution, abundance and diversity of the lotic desmids. Within a one-year sampling period, 148 species and 202 subspecific taxa of desmids were identified, representing 23 genera. Species of Cosmarium and Closterium accounted for approximately 70% of the desmids present, and were the most diverse and abundant taxa during all seasons except spring, when Hyalotheca dissiliens was the dominant desmid species. Average abundance and species richness generally were greatest during summer for both suspended and benthic desmids. Most desmids occurred in benthic habitats, and were randomly distributed among substrata. Average seasonal abundance was 7.4 × 104 cells·g?1 dry wt substratum, among 13 types of substrata. Highest desmid abundance was measured among substrata with intricate morphologies, such as Fontinalis spp., which was associated with 1.2 × 106 desmid cells·g?1 dry wt substratum, or 1.7 × 103 cells·cm?2 substratum. Cell division was observed for 70 desmid taxa, and average seasonal reproduction (based on cell numbers) among all substrata ranged from 4% in winter to 20% during summer. In addition, sexually produced zygospores were found occasionally for H. dissiliens. Desmids were distributed among most substrata examined in this stream, with abundance comparable to reported estimates from softwater lakes and acid bogs. In contrast to established dogma, lotic desmids are not incidental drift organisms, but rather comprise a viable and persistent component of the stream periphyton.  相似文献   

6.
Background: Estuaries are characterised by salinity gradients and regular flooding events. These environmental factors form stress gradients, along which species composition changes.

Aims: Analyse and compare patterns of plant species diversity along the estuarine salinity and flooding gradients of the Elbe and Connecticut Rivers.

Methods: Vegetation was sampled at three elevations (low, mid, high) in five sites of each marsh type (fresh, brackish, salt) in both estuaries. Patterns of species density (SD) and evenness (E) along the gradients were analysed and compared between the two estuaries with three-factor ANOVAs.

Results: The regional species pool was 33% higher for the Connecticut than for the Elbe. SD of fresh marshes (19 ± 2.2) was more than twice in the Connecticut than in the Elbe. We found an overall increase in SD from low to high elevation and from salt to freshwater marshes in both estuaries. However, SD and E were strongly depressed at intermediate elevations in the Elbe fresh and brackish marshes.

Conclusions: Although diversity patterns in the two estuaries show overall similarities, patterns of SD and E differ, when particular elevational zones and marsh types are compared. We hypothesise this to be due to evolutionary and historical influences on the regional species pools, shaping the impact of local biotic and abiotic processes.  相似文献   

7.
Jan Šťastný 《Biologia》2008,63(6):888-894
The distribution and ecology of desmids in wetland habitats in the Czech Republic were studied during 2003–2007. Samples were taken also from various aerophytic habitats and temporary pools thet had not been sufficiently studied before. Altogether 110 desmids taxa were found in 31 samples which were ordinated on the basis of their desmid species composition using a multivariate statistic method. The discussion focuses on the most interesting findings and on the factors that influence the distribution of desmids in different types of aerophytic habitats. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.  相似文献   

8.
Summary

A detailed study of the desmid flora of the area covered by the parish of Assynt, West Sutherland, has been made. Some 79 samples have been examined necessitating more than 1200 separate determinations of 291 taxa present. Amongst the desmids identified there are some extremely rare species and others newly recorded for the British Isles. The survey has shown that this sector of Sutherland is a prime area of the United Kingdom for the study of these fascinating and beautiful micro-algae.  相似文献   

9.
Gunnar Nygaard 《Hydrobiologia》1991,211(3):195-226
60 desmids were identified from plankton samples collected during 20 years, bimonthly, or monthly in 5 of the years. Only 5 desmids were perennial, performing cell divisions in a frozen lake at PAR at only 5 cal cm –2 day –1, below ice-cover. The greatest number of desmids per 100 ml lake water was found in September; it never exceeded 150. Owing to a concentration of free CO2 of only 0.02 mM l–1 and a HCO inf3 sup– concentration of 0.002 mM l–1 the densities of desmid cells were often smaller than 1 cell per 100 ml lake water. A density of 1 cell per 1 ml was attained only by Staurastrum longipes, a desmid showing temporal variation. The relation of the compound phytoplankton quotient to two components of the CO2-system is discussed. Three new taxa are described: Staurastrum brachiatum Ralfs var. bicorne n. var., Staurastrum thomassonii n.sp. and Xanthidium antilopaeum Kütz. f. bimaculatum n.f..  相似文献   

10.
Summary

Some very rare desmids, and others with previously undescribed characteristics have been identified from various locations in the British Isles.  相似文献   

11.
Photoaccumulations in light trap experiments have been studied in the desmids, Cosmarium, Micrasterias and Euastrum. Dependence of accumulation density on exposure time follows saturation curves, while dose response curves show optima. Time-lapse microcinematography and population methods have revealed that all three basic light-induced motor responses known in microorganisms participate in producing photoaccumulations in desmids. During the initial phase the cells are phototactically attracted towards the trap by scattered light. In low light intensity traps photokinetic reactions may play only a minor role, since photokinesis could be evoked only by light intensities100 lx in Cosmarium cucumis. True photophobic reactions have been demonstrated for the first time in desmids. There are two types of phobic responses in desmids: either the cell reverses its movement or it swings sidewise into the new direction. Behaviour of partially shadowed cells suggests that perception of light direction is brough about by simultaneous intensity measurement at two or more sites within the cell.  相似文献   

12.
In a survey employing epifluorescence microscopy with the DNA fluorochrome DAPI, associations between bacteria and filamentous desmids were found to be commonplace in acidic, Sphagnum-dominated Wisconsin peat-lands. Bacteria were associated with all genera of filamentous desmids encountered including Desmidium, Hyalotheca, Onychonema, Spondylosium, and Teilingia. Although only associations involving filamentous desmids having mucilaginous sheaths are illustrated here, bacteria were also noted on taxa lacking sheaths as well as some unicellular forms. Bacteria on Desmidium majus Lagerheim, D. grevillii (Kütz.) De Bary, and Hyalotheca dissiliens (Smith) Bréb. ex Ralfs tended to be concentrated in small pockets in the sheath material located near the isthmus and in the region between adjacent cells in the filament, whereas those associated with Spondylosium pulchrum (Bail.) Archer were more evenly distributed throughout the sheath. Most bacteria were rodshaped. Those associated with S. pulchrum, D. grevillii, and D. majus ranged from 1.1 to 11.2 μm in length. Bacteria within the sheaths of H. dissiliens and D. grevillii were Gram-negative. A second morphologically distinct population of bacteria was found at the sheath margin in D. majus and D. grevillii. Field collections containing filamentous desmids were examined with scanning electron microscopy and bacteria associated with Desmidium majus were investigated with transmission electron microscopy.  相似文献   

13.
Taxonomic diversity of desmids and other coccoid green algae is discussed in relation to different species concepts. For want of unambiguous criteria about species delimitation, no reliable estimations of global species richness can be given. Application of the biological species concept is seriously hampered by lack of sexual reproduction in many species. Molecular analyses demonstrated cases of close affiliation between morphologically highly different taxa and, contrary, examples of little relationship between morphologically similar taxa. Despite the fact that desmids and chlorococcal algae, because of their microbial nature, can be readily distributed, cosmopolitan species are relatively scarce. The geographic distribution of some well-recognizable morphospecies is discussed in detail. Of some species a recent extension of their area could be established, e.g., in the desmids Micrasterias americana and Euastrum germanicum, and in the chlorococcaleans Desmodesmus perforatus and Pediastrum simplex. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.  相似文献   

14.
《Plant Ecology & Diversity》2013,6(3-4):343-353
Background: Studies in temperate mountains suggest that plant–plant interactions modulate tree establishment above the forest line. In tropical mountains worldwide this issue remains largely unexplored.

Aims: To analyse the population structure and local spatial relationships of a dominant tree at a species-rich tropical Andean forest line.

Methods: We determined changes in the population structure of Diplostephium venezuelense along an elevation gradient between continuous forest and open páramo and analysed plant community structure and superficial rock cover in the neighbourhood of saplings and adults at the upper forest line.

Results: Sapling and adult densities were highest in low-altitude páramos adjacent to the forest line and at the borders of small forest islands. Saplings showed local spatial aggregation, were positively associated with small boulders and low shrubs, and negatively associated with mosses and lichens. However, no spatial association was found between scattered adults in the páramo and saplings of other forest trees.

Conclusions: Complex species-specific local spatial interactions, suggesting both facilitative and antagonistic effects, seem to modulate the establishment of the dominant tree D. venezuelense at and above the upper forest line. Nevertheless, the establishment of other tree species above continuous forests does not appear to be facilitated by the canopy cover offered by the isolated D. venezuelense individuals established in open páramo environments.  相似文献   

15.
5.1. According to the results from studying a broad variety of Estonian herbaceous communities (4.11) the question in 1.14 should be answered as:selection from a regional species pool into an actual species pool and selection from actual species pool into a microsite are mostly random and neutral processes and they are not directed significantly by interspecific competition. 5.2. Yet, the formation of a diversity pattern should be called aquasi-neutral process,mainly because the exclusion of species from communities due to asymmetric light competition is common during succession (when taller species outcompete shorter ones).  相似文献   

16.
Grazing effects were evaluated by comparisons between phytoplankton populations in the lake water and in bicompartmental chambers, deployedin situ in a Newfoundland lake. Micrograzing effects were evaluated separately from both the physical effects of macrograzers and the chemical effects of macrograzer metabolites on phytoplankton assemblages in bicompartmental chambers. Macrograzer metabolites were able to pass through fine gauze between the compartments. Thus, the chemical effects of the macrograzers were observed in one compartment while the physical effects were the dominant treatment in the other. Micrograzer effects were investigated in chambers without added macrograzers.Densities of some of the desmid species were depressed by the physical effects of macrograzers. This is the first ecological study to demonstrate such a grazing effect on desmids. Some individual taxa, such asArthrodesmus triangularis var.rotundatus (Raciborski)comb. nov., andMesotaenium sp. Nägeli (Zygnemaphyceae), were augmented under the chemical effects of macrograzer metabolites. Evidence suggests that the desmids were not micrograzed. Grazing effects on desmids have not previously been studied in waters in which they were abundant.The Chlorophyceae, which were small species in Hogan's pond, and the microflagellates generally maintained their overall population densities in spite of the presence of macrograzers, however, abundances of some individual species within the assemblages changed in the presence of macrograzers. Micrograzers may also affect the species composition and abundance of the individual chlorophycean taxa.With the exceptions ofSynedra sp. Ehrenberg andTabellaria fenestrata var.lacustris Meister the diatoms were unaffected by the grazers. The Chrysophyceae were little affected by micrograzing and physical effects of macrograzers, in contrast to chemical effects of macrograzer metabolites that were evident for individual species.Several of the Cyanobacteria (Cyanophyceae) were augmented in the presence of micrograzers. Evidence indicates that they were not micrograzed. Some individual species, e.g.,Microcystis aeruginosa Kützing, were augmented by both physical and chemical effects of macrograzers.  相似文献   

17.
A detailed qualitative investigation of the desmid community in the territory of the Province of Vojvodina (Northern Serbia, part of the Pannonian Plain) revealed a surprisingly high number of desmid taxa. Although most of the desmids were marked as rare, according to the results of physico-chemical analyses of water samples, several taxa were frequently recorded in habitats that are generally deemed unsuitable for desmids. The ecological characteristics of 18 desmid taxa, some of which known as acidophilic and/or oligotrophic, are briefly discussed. The unexpected presence of many desmid taxa is explained by assuming that their tolerance threshold to various physico-chemical parameters has changed considerably. Presented at the International Symposium Biology and Taxonomy of Green Algae V, Smolenice, June 26–29, 2007, Slovakia.  相似文献   

18.
Abstract

On 23 November 1976 we found a 270-cm-long leopard seal, Hydrurga leptonyx (de Blainville), resting on rocks 4 m from a 20 × 30-m pool in Seal Cove, on the east side of Main Island, The Snares.  相似文献   

19.
Abstract

A preliminary account on some mountain lakes of the Southern Apennines. Phytoplankton investigation on three ponds of the Monte Sirino (Basilicata).—Phytoplankton standing crop and species composition have been studied in three ponds of the Southern Apennines. The observations carried out throughout ten months in 1975, showed a great number of species present in the Remmo pond, mainly diatoms, desmids, green algae, and blue-green algae. In the Sirino pond only diatoms and Chrysophyceae were present.

In comparison, in the Zapano pond, the phytoplankton was scarcely represented but the occurrence of some species of green algae may suggest a eutrophic water condition. On the basis of the peculiarities both of species composition and biomass, the major water bodies may be considered oligotrophic.  相似文献   

20.
Forty-seven species of desmids, representing all four families, were examined for the presence of the xanthophyll loroxanthin by reverse-phase high-performance liquid chromatography. In the Desmidiaceae 28 of the 35 species examined possessed loroxanthin, and in the Mesotaeniaceae two of the six examined had loroxanthin present. All six species of the families Peniaceae and Closteriaceae examined possessed loroxanthin. Although the distribution of loroxanthin appears to be disjunct in the desmids and does not have strict taxonomic significance, it does follow a coherent pattern consistent with current ideas on desmid phylogeny. This pattern suggests that loroxanthin synthesis probably evolved once in the desmid lineage, with one or more subsequent reversals.  相似文献   

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