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1.
A study of communities of attached algae in Lake Mize Florida, wax made during July 1969, July-August 1970 and April 1971. The substrates exposed during the study included glass slides mid the terrestrial form of the amphibious sedge, Eleocharis baldwinii (Torr.) Chapman. Counts were used to determine the relative abundance and densities of the species present on the 2 substrates under different environmental conditions. Such analyses indicated that at any given lime and place, a number of factors influenced the composition of the periphyton. Generally, lightly adhering, resupinate species attained higher densities on glass slides than filamentous and loosely associated metaphytonic species. The epiphytic flora of E. baldwinii contained a large number of both strong attachers and the metaphyton. The vertical range of many attached species was also greater on E. baldwinii than on glass slides.  相似文献   

2.
Benthic diatoms form a particularly important community in oligotrophic lakes, but factors influencing their distribution are not well known. This study reports the depth distribution of living motile and total diatoms (living plus dead diatoms) on both natural (from sand to fine organic mud) and artificial substrates in an oligotrophic lake. On artificial substrates, motile diatom densities peaked in abundance (24–30 cells · mm?2) between 0.6 and 1.9 m depth; on natural sediment surfaces, motile diatoms were generally more numerous and peaked in abundance (925 cells · mm?2) at 1.3 m depth. Total diatom densities on artificial substrates were highest (1260 valves · mm?2) at 0.6 m depth, with very low values below 3 m depth; on natural sediment surfaces, total diatom abundances were generally much higher (21600 valves · mm?2) at 3 m depth and declined gradually with depth. Significant relationships were found between light and diatom densities on the artificial substrate. Ordination analysis indicated that substrate type significantly correlated with the variation of diatom composition on artificial and natural substrates. Our results suggest that in oligotrophic lakes, light influences benthic diatom abundance, whereas substrate type has more influence on benthic diatom composition.  相似文献   

3.
Chemically inert, cylindrical rods positioned in the littoral of two eutrophic Alberta lakes supported higher periphytic algal biomass (measured as total chlorophyll a) than nearby morphologically similar culms of Scirpus validus Vahl. during most of the summer. Upon initiation of macrophyte senescence, biomass on the two substrata became more similar. Experiments were conducted to investigate the basis for these observations. Whole extracts of intact vegetative Scirpus culms had no effect on periphyton photosynthesis, suggesting that the natural substrata do not produce water-soluble allelochemicals. Various modifications of the rod surfaces (roughening, wax coating, wax color) were used to test whether surficial properties of Scirpus culms influenced periphyton accumulation. Roughened rods supported levels of biomass similar to those of smooth rods, and both substrata developed structurally complex periphyton communities. Rods covered with paraffin wax had periphyton communities that were lower in biomass and structurally more simple than those on un-coated rods or on Scirpus culms. Coloring of the wax coating had no consistent effect on periphyton accumulation. We hypothesize that the hydrophobic cuticle on actively growing Scirpus culms retards the development of precursors for attachment by periphytic algae. Upon senescence of the culm and loss of epidermal integrity, colonization of culm surfaces by periphytic algae may occur in a manner similar to that on artificial substrata.  相似文献   

4.
Buffalo Creek is in a forested watershed in eastern Pennsylvania and is relatively acid in upstream reaches (pH~6), becoming alkaline downstream (pH~8). Temperature, nitrogen (NO3-N) and phosphorus (O-PO4) increase significantly downstream whereas N/P declines. Nutrient-diffusing substrata were deployed in triplicate at an upstream and downstream site. Six treatments included two concentrations of nitrate, two concentrations of phosphate, nitrogen + phosphate, and a control. Substrata were collected after 18 days, scraped and analyzed for accrual of chlorophyll a and algal community structure. Chlorophyll a and algal biovolume were greatest downstream across all nutrient treatments. At the community level, accrual appeared to be limited by phosphorus at upstream sites. Downstream accrual also may have been phosphorus-limited, but the results were equivocal. Benthic algae on all treatments at both sites were ~96% diatoms. Minimal overlap in species composition was observed between upstream and downstream sites. Of the 75 species of diatoms encountered in the study, 58 species did not occur at the upstream site and 10 species did not occur at the downstream site. The upstream site was depauperate in species and dominated by Eunotia exigua (Bréb. ex Kütz.) Rabh., which showed a positive response to phosphorus and accounted for over 50% of the biomass across treatments. The downstream site showed a four-fold increase in species richness. Communities at this site contained some species that appeared to be phosphorus-limited, e.g. Melosira varians Ag., and others that seemed to be nitrogen-limited, e.g. Diatoma vulgare Bory and Navicula seminulum Grun. We conclude that extreme conditions upstream (low pH, high N/P) result in a species-poor community dominated by acidophilous phosphorus-limited diatoms. Increases in downstream nutrients and pH result in a relatively rich and diverse community.  相似文献   

5.
The growth rates of 12 strains of attached freshwater diatoms were examined as a function of irradiance. The results were used to determine physiological parameters in the growth–irradiance relationships. Values of G max (maximum growth rate) and I  k (irradiance at half of G max) correlated with successional phase. The development of attached diatom communities appears to proceed from high irradiance species to low irradiance species that appear later in the successional sequence. Thus, efficiency of light use is linked to successional strategy, as has been documented for terrestrial plants.  相似文献   

6.
生化他感作用与高寒草甸上人工草场自然退化现象的研究   总被引:30,自引:4,他引:30  
细叶亚菊是海北地区垂穗披碱草人工草场上主要入侵杂草之一。本文探讨了垂穗披碱草和细叶亚菊草种间抑制与促进作用以及细叶亚菊各种代谢产物对垂穗披碱草种子萌发与幼苗生长的抑制作用。实验表明:在垂穗披碱草人工草场自然退化过程中存在着生化他感作用。牧草的自然退化速度与主要杂草入侵程度呈明显的相关性。  相似文献   

7.
The photosynthetic activity of different algal communities at the outer edge of an Equisetum fluviatile L. stand in an oligotrophic lake (Pääjärvi, in southern Finland) was investigated. Production by the algal communities was measured simultaneously using a modified 14C-method, and the results were related to the volume of algae and the available irradiance. The relative production rate (P/B quotient) of phytoplankton was ca. 3 × that of epiphyton and ca. 20 × that of epipelon. Epiphyton productivity remained almost constant although the algal volume varied greatly, suggesting that the surface layer of the algal community was mainly responsible for the photosynthetic activity. In the littoral area (at 1 m depth) primary production/m2 of lake surface by phytoplankton, epiphyton and epipelon was similar but in the littoriprofundal area (2–4 m) phytoplankton production was twice that of epipelon. Primary productivity of epiphyton and epipelon/m2 of substratum was about equal to phytoplankton productivity/m3 of water at the same irradiance. This relation provided a means of estimating the relative contributions of the different algal communities to the total algal production in the lake.  相似文献   

8.
Light and scanning electron microscopy were utilized to quality diatom colonization in Oak Creek, Arizona. Aluminum SEM stubs with and without plexiglass discs were anchored into rocks. Early colonization on five stub microzones was examined at hourly intervals; weekly intervals of up to 3 wk were employed to record community development in pool find riffle. Plexiglass was more suitable for microbial colonization than aluminum. Organic matter and bacteria were important surface pre-conditioning agents while fungi were instrumental in trap/ting cells during early stages of colonization in the riffle. Diatom colonization was initialed within 1 h on the upstream side of substrata in riffles, while the tap face was colonized first in pools. Colonization moved rapidly to the perimeter in each system. Early colonization of-side microzones was considerably more asymmetric in the riffle than, pool. At Idler stages (2 wk) diatoms with their associated mucilage and algal filaments contributed to the stability of the microbial communities. Horizontally positioned species (Achnanthes, Cocconeis) were early colonizers in both systems while vertically positioned species (Gomphonema, Nitzschia) were more important in later successional stages (3 wk) in the riffle. Horizontally positioned species remained dominant throughout the 3 wk period in the pool. After 3 wk, diversity was normally greater in the pool while density was higher in the riffle. Detrital microcosms containing viable microbiol assemblages frequently collected on tin-upstream face of substrata in the riffle. The random nature by which these detrital microcoms contact downstream substrata greatly contribute to the spatial variation of periphyton in streams. These detrital microcosms expedite repeated colonization in lotic systems.  相似文献   

9.
Light and electron microscopy were used to investigate the complex structure of the frustule of Paralia sulcata (Ehrenb.) Cleve. Rimoportulae are reported for the first time in this diatom and two types of linking processes are described. The ease with which the cingulum is lost is explained with regard to its attachment to the valve. Two kinds of heterovalvy were observed and the taxonomic significance of one of these is discussed. The validity of Heiberg's genus Paralia is confirmed and a type slide of the species is designated.  相似文献   

10.
Experimental field manipulations of artificial substrata were used to examine the mechanisms controlling attached algal zonation down the face of the dam in Lake McConaughy, a large reservoir in western Nabraska. Sets of clay tiles were incubated in the upper (2.5 m depth) and lower (8 m depth) growth zones for two weeks. Five sets tiles were then switched from the upper to the lower growth zone and vice versa. Five additional sets of tiles were switched to the lower zone and artificially disturbed. Diatom cell densities increased rapidly in both the zones; however, wind-induced turbulence caused dramatic declines (up to 61%) in densities in the upper zone. Consequently, cell densities in the upper and lower growth zones were not significantly different after four weeks, despite the 17–30% higher light levels in the upper zone. Based on cell densities and relative abundances on clay tiles and naturally occurring rocks, 26 of the 32 most common diatom taxa had a significant upper (10) or lower (16) zone preference. Of these, 15 taxa exhibited a consistent response to one or both switching manipulations, confirming a growth zone preference, and two showed a clear preference for disturbed substrata. Diatom growth form appeared to play a major role in determining the vertical zonation of attached communities, since actively motile taxa exhibited a lower zone preference and stalked forms occurred primarily in the upper zone. The present study indicates that light attenuation and wave disturbance are primary mechanisms that control the vertical zonation of freshwater epilithic algae.  相似文献   

11.
Two sets of experiments were done to quantify the effects of chronic copper exposure on natural peri‐ phyton in a nonpolluted calcareous river. The results of short‐term (up to 6 h exposure) experiments corroborated the significance of pH on copper toxicity. Copper toxicity increased when pH was reduced from 8.6 to 7.7, and this was related to the effect of pH on copper speciation (free copper concentration increased from 0.2% to 2.3% of total copper). Longer term experiments demonstrated that periphyton communities exposed to copper under pH variation (8.2–8.6) were already affected at 10 μg·L ? 1 (20–80 ng·L ? 1 Cu2 + ) after 12 days of exposure. Copper exposure caused stronger effects on structural (algal biomass and community structure) than on functional (photosynthetic efficiency) parameters of peri‐ phyton. Changes in community composition included the enhancement of some taxa (Gomphonema gracile), the inhibition of others (Fragilaria capucina and Phormidium sp.), and the appearance of filament malformations (Mougeotia sp.). The results of our study demonstrated that several weeks of exposure to copper (10–20 μg·L ? 1) were sufficient to cause chronic changes in the periphyton of oligotrophic calcareous rivers. This degree of copper pollution can be commonly found in the Mediterranean region as a result of agricultural practices and farming activities.  相似文献   

12.
Community dynamics of epiphytic diatoms were studied for 3 years in a chronically and an episodically acidified tributary of Buck Creek, Adirondacks. Both streams experienced pulses of acidity during hydrologic events but these pulses were more pronounced in the episodically acidified stream, where pH decreased over two units (between 4.53 and 6.62) and the acid‐neutralizing capacity (ANC) became negative. In the chronically acidified stream, pH was below 4.9 and the ANC was negative 94% of the time. In this stream, high inorganic acidity following SO42? enrichment from snowmelt or rainstorms alternated with high organic acidity derived from a headwaters wetland during base flow. The fluctuating water chemistry generated shifts in diatom community composition: from exclusive dominance of Eunotia bilunaris (Ehrenberg) Mills during periods of high inorganic acidity to proliferation of several subdominant species during periods of high organic acidity. In the episodically acidified stream, the pulses of acidity were associated with high NO3? concentrations and the corresponding high ratios of inorganic monomeric Al (Alim) to organic monomeric Al (Alom). Diatom communities there were dominated exclusively by E. exigua (Brébisson) Rabenhorst year round; however, this species peaked during periods of low acidity. Periods of high acidity and Alim:Alom ratios were marked by a decline in E. exigua and a concomitant increase in the subdominant species. Variance partitioning into terms of environmental and temporal variance, and their covariance, suggested that diatom communities in the chronically acidic stream were governed primarily by environmental factors while in the episodically acidic stream environmental and temporal factors had equal contributions.  相似文献   

13.
We studied the hypothesis that diatom immigration abilities are related to their fitness for colonizing stream substrates. Diatom abundances on artificial substrates exposed for 24 h (the measure of immigration rate) and abundances of stream plankton were determined in six habitats. Diatom immigration varied among habitats from 50–2500 cells·cm?2·d?1. Immigration rates decreased 10-fold with increases in current from 10 to 30 cm·s?1 but changed little during a 40-d summer period. Immigration abilities of diatom taxa were characterized as ratios of either their abundances or relative abundances in immigration assemblages versus in the plankton. Immigration abilities varied over 100-fold among different species. Immigration of some species could be characterized as slower than others in different streams; however, variation in immigration abilities of other species among streams indicated that environment also affected immigration. Diurnal variation in abundance and species composition of the immigration pool (stream plankton) can be important in assessing immigration abilities. Immigration ability may affect benthic diatom fitness. Monoraphid diatoms had a lower probability of immigrating from the plankton than araphid diatoms.  相似文献   

14.
The effects of herbivore size and hunger level were tested on lotic periphyton community structure and ash-free dry mass (AFDM). My hypotheses were 1) that small herbivores would remove more periphyton per unit biomass than large herbivores of the same species because of energetic demands and 2) that within the same size class, starved herbivores would remove more periphyton than nonstarved herbivores. The herbivore used was the prosobranch snail Elimia clavaeformis Lea. Seven treatments were employed: 1) no snails (control); 2) small “starved” snails; 3) large “starved” snails; 4) small and large “starved” snails; 5) small fed snails; 6) large fed snails; and 7) small and large fed snails. Although snails removed significant amounts of periphyton AFDM relative to controls, neither snail size nor degree of starvation had a significant effect on loss of total AFDM. Small snails removed significantly more erect forms of Stigeoclonium tenue (C. A. Ag.) Kütz. than large snails, but snail size had no other significant effect. Starved snails removed significantly more Cocconeis placentula Ehr. than fed snails, suggesting that after the more susceptible growth forms (e.g. erect Stigeoclonium) were removed, Cocconeis cells became more vulnerable to grazing by hungry snails. When small and large snails were combined in chambers, large snails gained weight over time, whereas small snails lost weight. These results suggest that intraspecific competition may occur within populations of Elimia.  相似文献   

15.
Navicula ulvacea (Berkeley ex Kütz.) P. T. Cleve, a marine colonial blade-forming diatom originally discovered in Scotland was collected at North Rustico, Prince Edward Island, during winter 1971. It formed dense stands of Porphyra-like fronds, ranging up to 60 mm long × 20 mm wide. These occurred under ice-covered water on rocks 1–2 m below zero tide. Comparisons made at the light and scanning electron microscope level compared favorably with original Aberdeen material. Clonal cultures established from single cells at first also formed blades, but rarely more than 10 mm long. In numerous serial subcultures made since 1971 no further blades have been formed. Instead, growth consisted of well-separated cells or short filaments scattered over the bottom and sides of the vessels. Older cultures developed prostrate sheets of filaments, embedded in a mucilagenous matrix and occasional bubble-like eruptions. Results of the cultures suggest that N. ulvacea probably occurs in a prostrate form in nature, perhaps more commonly than in the blade form. Literature records since the original collection in 1844 are brought together but are considered doubtful. A discussion on nomenclature is included.  相似文献   

16.
A new species of the diatom genus Eunotia is described. The species, E. catillifera Morrow, is distinguished by the presence of fin-like plates, or transapical ridges, which alternate with the striae on the valve faces. This alga appears to be intermediate between the more typical Eunotia species and Semiorbis Patr. This observation suggests that Semiorbis hemicyclus (Ehr.) Patr. in Patrick and Reimer be returned to Eunotia hemicyclus Ralfs in Pritchard and that the use of the generic name Semiorbis be discontinued.  相似文献   

17.
The centric diatom, Thalassiosira weissflogii Grun., can be induced to undergo spermatogenesis by exposing cells maintained at saturating levels of continuous light to either dim light or darkness. Using flow cytometry to determine the relative DNA and chlorophyll content per cell, the number of cells within a population that responded to and induction signal was measured. From 0 to over 90% of a population differentiated into male gametes depending upon both the induction trigger and the population examined, regardless of the average cell size of the population. Through the use of synchromized cultures, we demonstrated that responsiveness to an induction trigger was a function of cell cycle stage; cells in early G1 were not yet committed to complete mitosis and were induced to form male gametes, whereas cells further along in their cell cycle were unresponsive to these same cues. A simple model combining the influence of light on the mitotic cell cycle and on the induction of spermatogenesis is proposed to explain the observed diversity in population responses to changes in light conditions.  相似文献   

18.
运用分形模型研究了川南天然常绿阔叶林及其人工更新成檫木(Sassafras tzumu)林、柳杉(Cryptomeria fortunei)林和水杉(Metasequoia glyptostroboides)林后土壤团粒结构,探讨了分形维数与林地土壤水源涵养功能、肥力特征和微生物数量之间的关系。结果表明:天然常绿阔叶林人工更新后土壤团粒结构的分形维数和结构体破坏率增大、土壤物理性质变差、养分含量和微生物数量降低,3种人工林中,檫木林较好、水杉林次之、柳杉林最差;土壤团聚体、水稳性团聚体和水稳性大团聚体含量越高分形维数越小;在湿筛条件下,土壤结构体破坏率随分形维数的降低而减小;土壤团粒结构的分形维数与土壤物理性质、养分含量和微生物数量之间存在显著的回归关系。这表明天然常绿阔叶林人工更新后由于不同林分对林地土壤组成结构的维护效果不同,导致更新后林地土壤物理、化学和生物性质变化,林地土壤团粒结构的变化,进而影响其分形维数的大小。因此,分形维数可作为天然常绿阔叶林及其人工更新后林地土壤水源涵养功能、肥力特征和微生物活动情况的一项综合性定量化评价指标。同时,为保护天然常绿阔叶林、选择适宜的更新树种和天然常绿阔叶林人工更新后林地土壤的科学管理提供依据,也为退耕还林中树种的选择提供参考。  相似文献   

19.
The morphology and sexual reproduction of the attached diatom Cocconeis scutellum Ehr. var. scutellum have been investigated using field and culture materials. The diatom grew well at 14–22° C and in a medium using enriched full strength seawater or 50% diluted seawater. One gamete was formed without cytokinesis in a gametangium and one auxospore arose from paired gametangia. The size of gametangia and initial cells were 17.8–29.9 μm and 43.3–59.5 μm, respectively. Valve width decreased linearly with decreasing valve length. The regression coefficient between them was invariable with the change of the environment. The transapical striation densities were 7–12 and 7.5–13.5 in 10 μm in araphid and raphid valves, respectively. The density showed a tendency to increase with decreasing valve length in both valves. The densities in both valves, except the small araphid valve, are invariable with the change of the environment. The relationships between valve length and width, and between valve length and striation density have been compared with those of taxa allied to C. scutellum var. scutellum. It is concluded that C. scutellum var. scutellum, as usually delimited, is a heterogenous taxon.  相似文献   

20.
Blue-green light increased the chlorophyll concentration and chloroplast number of cells of Stephanopyxis turris (Grev.) Ralfs, compared to white light controls. Light fields for growth were 400 μW·cm?2 (12:12 LD cycles). Chlorophyll increased up to 100%/cell, but no change in the ratio of chlorophylls to major carotenoids occurred. The effect was, therefore, not that of complementary chromatic adaptation. At the same time, blue-green light enhanced the photosynthetic fixation of CO2. At the ultrastructure level, an increase in, and rearrangement of, the thylakoid system occurred.  相似文献   

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