ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00001.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTNostocis a genus of filamentous cyanobacteria that can form macroscopic or microscopic colonies and is common in both terrestrial and aquatic habitats. Much of the success ofNostocin terrestrial habitats is related to its ability to remain desiccated for months or years and fully recover metabolic activity within hours to days after re‐hydration with liquid water. Nostoccan also withstand repeated cycles of freezing and thawing and, thus, is an important component of extreme terrestrial habitats in the Arctic and Antarctic. The ability to fix atmospheric N2can provide an advantage in nitrogen‐poor environments. Nostocalso has the ability to screen damaging ultraviolet light in terrestrial and shallow benthic habitats. The genus potentially could be important in paddy rice culture because it fixes nitrogen that may later be released and used by plants; it also may play a role in soil formation and may increase nitrogen input to natural aquatic and terrestrial ecosystems. The abilities to survive in terrestrial habitats and fix N2are important in symbiotic interactions with fungi (lichens), liverworts, hornworts, mosses, ferns, cycads, and the angiospermGunnera. Nostocis somewhat resistant to predation; this probably is related to production of large amounts of sheath material, synthesis of microcystin‐like toxins by some strains, and formation of colonies that are too large for many algivores to consume. Some organisms can subsist onNostoc,although it may not be a preferred food source. Lytic cyanophages also infectNostoc,but little is known about population control ofNostocin its natural environment, Late Precambrian fossils resemblingNostochave been described, andNostocpossibly has been an important component of many terrestrial and aquatic communities since that

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00002.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe marine chrysophyteDinobryon balticum (Schzütt) Lemm. was one of the dominant members of the phytoplankton community (1.8×103cells‐L−1) in June and July in Conception Bay, Newfoundland. Dinobryon balticumcolonies were common only in samples from June and July. The cells were concentrated at 5 m (X±SD=1.11±4 × 105cells.L−1) and at 40 m (3.32±2×104.L−1) depths. Colonies were composed of up to 560 cells with a mean (±SD) colony size of 10 ± 1 cells at 5 m and 40 ± 8 cells at 40 m. Fluorescent latex bead‐uptake experiments conducted with field samples indicated that this marine species was capable of phagotrophy and that twice as manyDinobryoncells were ingesting beads at 40 m than at 5 m, although the ingestion rates for those cells actively ingesting beads were similar at both depths. This chrysophyte was found in association with bacteria‐and nutrient‐rich microhabitats of microaggregates and fecal pellets. The cells and colonies observed in this study appeared to be healthy, as demonstrated by their appearance and their

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00019.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTUltraviolet‐B radiation (UVBR: 290‐320 nm) inhibited ammonium uptake (pNH4) and nitrate uptake (pNO3) in natural plankton assemblages collected during a transect from 37° N to 55° N in the Pacific Ocean. Comparison of responses in pNH4to ambient solar‐ and lamp‐enhanced UVBR spectra allowed calculation of an action spectrum for pNH4inhibition. The slope of the action spectrum for Pnh4is half as steep as action spectra for UVBR inhibition of photosynthetic carbon uptake. Consequently, WBR‐induced photoinhibition of pNH4extends to greater depths than inhibition of carbon fixation due to the greater relative effect of longer UVBR wavelengths. Inhibition of pNH4was dependent upon UVBR dose when doses were weighted by the pNH4action spectrum. Dependence of WBR inhibition of pNH4on dose rate was not apparent. We found that near‐surface pNH4and pNO3can be overestimated in excess of 50% when measured using standard incubation vessels made of UVBR‐absorbing materials such a

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00025.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe community structure and productivity of epiphytic microalgae on field populations of eelgrass(Zostera marinaL.) from a high flow regime were characterized under water‐column nitrate enrichment over a 30–d period during the autumn growing season for the macrophyte. Epiphyte communities in replicate low‐nitrogen sites(LOW‐N,median water‐column nitrate concentrations below detection) were compared to communities in replicate N‐enriched sites wherein nitrate was leached from clay pots filled with enriched agar(N‐ENRICH,median concentration ca. 6 μM NO3−‐N; pots replaced at 8– to 12–d intervals). In experimental chambers, total epiphyte community productivity as14C‐bicarbonate uptake was determined from short‐term (3–h) laboratory assays. Track light microscope‐autoradiography enabled estimates of species‐specific productivity for abundant algal taxa. After 6 d in theLOW‐NandN‐ENRICHcommunities, the crustose adnate red algaSahlingia subintegra (Rosenvinge) Kornmann was dominant in terms of cell number and codominant in biovolume. Photosynthetic dinoflagellates, not previously reported as abundant in eelgrass epiphyte communities, were dominant in biovolume contribution after both 6 and 30 d inLOW‐Ncommunities. Nitrate enrichment stimulated the adnate monoraphid diatomCocconeis placentulaEhr. but apparently inhibited dinoflagellates and the diatomMelosirasp. Total productivity of the epiphyte communities remained comparable in both theLOW‐NandN‐ENRICHsites. Shifts in community structure and species‐specific productivity, however, indicated a controlling influence of nitrate supply on microalg

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00036.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe role of environmental factors in seasonal succession of six clones of marine diatoms was examined by testing effects of various combinations of temperature (5°, 10°, 15°, 20°C) and photoperiod (10, 12, 14, 16 h) on time to germination of resting stages and subsequent vegetative cell division rates. Resting stages were induced in batch cultures using a low nutrient medium and a cold, dark period. A three‐factor ANOVA showed that species, temperature, daylength, and their interactions signficantly(P =0.0001) injuenced germination time and division rate. Resting stages ofChaetoceros similisCleve andOdontella aurita (Lyngbye) Agardh were most successful in producing populations of cells on warm, long days (20°C/16 h). Chaetoceros didymusEhrenberg andC. cinctusGran were most successful under more moderate conditions (15°C/14 h). Resting stagesof Ditylum bright‐wellii (West) Grunow germinated and cells divided rapidly under all conditions. No consistent pattern was evident withThalassiosira rotulaMeunier. We compared results of the laboratory study with environmental conditions prevailing during the presence of these species in a British Columbia fjord. Favorable growth conditions determined forC. didymus, D. brightwellii,andT. rotulawere similar to conditions present when these species were commonly found in

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00044.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSeveral experiments were conducted to understand better the physiological mechanisms underlying growth inhibition of the dinoflagellateGonyaulax polyedraStein due to small‐scale turbulence shear. To measure photosynthetic14C uptake, a “phytoplankton wheel” device for rotating cultures in closed bottles was used. Turbulence was quantified biologically in the bottles by comparing growth inhibition with that in cultures with constant shear between a fixed cylinder and an outer concentric rotating cylinder (a stable Couette flow). At saturating irradiances, particulate photosynthesis (Psat) or photosynthesis per unit chlorophyll (PBsat) were not inhibited completely at the highest turbulence level (26.6 rad.s−1), and photosynthesis was less sensitive than growth. Photosynthesis per cell (PCsat) was increased by turbulence. In three experiments on the effects of turbulence on photosynthesis versus irradiance curves, the slope of the curve, α, for particulate photosynthesis at limiting irradiances did not change. Photosynthesis per unit chlorophyll per unit irradiance (αB) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, αC, increased with turbulence, suggesting an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbulence, and in one experiment excretion of photosynthetically fixed14C was not affected by motion. Ratios of accessory pigments to chlorophylladid not change with turbulence, but pigments per cell and per dry weight increased with turbulence. These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was applied for 1 week, β‐carotene increased while peridinin and diadinoxanthin decreased, suggesting inhibition of synthesis of these latter pigments by prolonged turbulence. Since cell numbers did not increase or decreased during turbulent 72–h incubations, cell division was inhibited and also the cells were very much enlarged. Increases in αCper cell suggest that, in the sea, photo synthetic metabolism can persist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly rapidly in the ocean depending on the degree of wave‐ and wind

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00050.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTEpiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from 35 study ponds on CapeHerschel (78°37″N, 74°42″W), east‐central Ellesmere Island, Canada. All the sites are shallow (maximum depth<2 m), clear, oligotrophic, and freshwater. The ponds freeze completely for 10 months of the year. Major ion concentrations are relatively similar among the 35 sites, although environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in species composition were evident among the ponds. Moreover, many of the diatoms exhibited varying degrees of microhabitat specificity. Variance partitioning by canonical correspondence analysis showed that 26% of the total variance exhibited by diatom species composition could be accounted for by the measured environmental variables (i.e. 10.2% by habitat and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibration were used to develop a transfer function to infer pondwater alkalinity from the diatom assemblages. Other important environmental variables included [Na+] for the epilithic and [SiO2] for the epiphytic asse

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00060.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe dynamics of chrysophyte populations and the onset of encystment in relation to several physical, chemical, and biological variables were studied in two Canadian lakes, Lake Opinicon (LO) and Upper Rock Lake (URL). LO is shallow and polymictic during the ice‐free season, whereas URL is deep and dimictic. Seasonal patterns of many limnological variables, as well as species composition and seasonal dynamics of chrysophyte assemblages, were broadly similar in both lakes. Three groups of chrysophytes were recognized: 1) taxa that were more abundant during ice cover and/or early spring and occasionally in late fall(Dinobryonspp. Ehrenberg andSynura spinosaKorsh), 2) taxa that seemed to prefer moderately warm waterproglena americanaCalkins andOchromonassp. Wyssotzki) and had maximum densities in late summer and occasionally in the fall, and 3) taxa that occurred in low numbers and did not exhibit any discernible seasonality in the two lakes(Mallomonasspp. Perty). Encystment rarely occurred during ice cover in both lakes. Stomatocyst concentrations were highest shortly after ice breakup (late April or early May), declined to trace levels by June, and remained at those levels until the end of the sampling season(late November). Encystment rates (cyst concentrations) were higher in dimictic URL. Encystment in both lakes coincided with concurrent changes in physical and chemical variables and chrysophyte vegetative cell densities, but it was not possible to pinpoint the exact conditions responsible for triggering encystment. Only a small proportion of chrysophytes encysted. Cyst production within a lake may vary from year to yea

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00070.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWe examined the physiology and biochemistry associated with the iron‐limited continuous culture of the halotolerant cyanobacteriumSynechococcusPCC 7002. Biomass production, photosynthetic pigment levels, photosynthetic efficiency, and the production of hydroxamate‐ and catechol‐type siderophores are reported for cells grown over a range of available iron concentrations. The relationship between the yield ofSynechococcusPCC 7002 in iron‐limited chemostats and the concentration of available iron was not linear. SynechococcusPCC 7002 expressed an inducible physiological response that led to alterations either in the cellular iron quotient or, more likely, in levels of available iron due to induced iron‐scavenging processes. During iron limitation these cyanobacteria produced components consistent with the activation of a high‐affinity iron transport system; both hydroxamate‐ and catechol‐type siderophores were detected. Iron‐limitedSynechococcusPCC 7002 also reduced CO2fixation rates from luxury levels to a rate that matched the cellular growth rate, presenting interesting implications for oceanic c

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1995.00079.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY