摘要:

ABSTRACTThe unidirectional water flow to which stream macro‐algae are exposed imposes mechanical strseses that vary with the life‐form of the algae. The stress, and thus the possibility of breaking or detaching with loss of previously accumulated resources, is least in the boundary‐layer forms (crusts, turfs) and greatest in the semierect forms (mucilaginous and nonmucilaginous filaments, and tissuelike thalli). Present evidence on the resource costs of providing semierect forms with the observed safety factor in minimizing the chance of breakage under normal flow conditions does not permit useful comparisons to be made with resource acquisition benefits of exposure to rapid water flow. These benefits relate to minimizing boundary‐layer thickness, with a consequent increase in the potential flux of nutrient solutes to the algal surface. Such enhanced fluxes are significant in habitats in which (as is often the case) algal growth is nutrient‐limited. By contrast, crusts and turfs have lower potential nutrient fluxes due to the thick boundary layers around the substratum to which they are attached. A possible advantage for resource acquisition of the thick boundary layers associated with crusts and turfs relates to the use of extracellular catalysis by the alga of the conversion of the supplied form of nutrient (e.g. HCO3‐, organic P, Fe3+) into the form taken up (CO2, inorganic P, Fe2+, respectively). A thick boundary layer restricts the loss of the transformed nutrient species to the bulk, rapidly flowing medium thus favoring uptake of CO2, inorganic P, or Fe2+. The influence of the stream on photosynthesis and growth via light supply involves shading by riparian vegetation and shading of low‐growing algae (crusts and turfs) by semierect algae as well as by semierect submerged bryophytes and tracheophytes. The shading of boundary‐layer forms by semierect plants further constrains the photo synthetic rate achievedin situby crusts and turfs. The negative effect of shading on productivity is mitigated by the generally low (less than 25% of full sunlight) photon flux density needed for photosyn‐thetic (and net productivity) saturation of stream macro‐algae, especially when nutirents are limiting. There is relatively little acclimation to changed total photon flux density and its spectral distribution within the natural range. Problems of upstream migration could be partially resolved by herbivorous motile animals as vectors. Despite potential problems for grazers on semierect algae due to rapid water movement, it is not clear that such algae are less grazed than crusts or turfs. Further work in certain areas could yield important results using currently available techniques. Examples are 1) the role of water flow per se (independent of boundary layer effects) on growth, 2) the allocation of resources to structural elements as a function of water flow, 3) the effect of flow on bidirectional transmembrane fluxes (influx and efflux measured with tracers) of nutrients (corrected for boundary‐layer effects), and 4) the role of animal vectors in upstream dispersal. Positive results in 1–3, that is, an effect of increased flow on growth, resource allocation, and transplasmalemma fluxes, could indicate a role for mechanosensitive (= stretch‐sensitive) ion channels and other m

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00133.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTIsolates of the centric diatom,Thalassiosira weissflogiiGrun., were maintained in exponential growth under constant, favorable conditions for nearly 2 years. During this interval, each culture underwent periodic increases and decreases in mean cell size, a behavior predicted for diatom populations alternating between sexual and asexual reproduction, respectively. The overall patterns of cell size change displayed by each culture, however, were unique. The maximum size of newly enlarged cells varied among isolates and within a given isolate over time. Consequently, both the timing and rate of increase in mean cell size also varied despite the fact that the minimum average cell size obtained by the various cultures was relatively constant. The most consistent feature among the isolates was the rate of decrease in mean cell size, a value determined by the physical constraints of the diatom frustule during mitotic divisions. We hypothesize that the extent of the variability exhibited by these cultures results from the fact that an inherent feature of diatom populations is a constantly changing genetic composition.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00146.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTMorphological variability of intertidalChondrus crispusStackh. fronds along a small open rocky coast was related to wave exposure and emersion. Cluster analysis revealed two well‐defined morphologies: filiform and planiform, named the N morphotype and B morphotype, respectively. We propose a rapid method of classifying fronds based on the morphology of the cross section at half the height on the thallus. The N morphotype is characterized by fewer dichotomies per unit length, a circular cross section with a large inner cortex, and narrow fronds. It is abundant at low intertidal and exposed sites. The B morphotype is characterized by more dichotomies, smaller sizes, a subelliptical or flattened cross section, and broad fronds. It is abundant at high intertidal sites in sheltered areas. Regression analysis revealed a major effect of water movements on frond morphology with respect to tidal level, which was more evident at high intertidal levels. No relationships were observed between morphology and life history phase

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00156.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe relationships between 23 scaled chrysophyte taxa (Chrysophyceae and Synurophyceae) and measured limnological variables in 62 Adirondack, New York, drainage lakes were examined by canonical correspondence analysis (CCA). The major proportion of variation in chrysophyte species distributions was strongly related to total monomeric Al (Alm) and Mg concentrations, and their close correlates pH, Na, Ca, and acid‐neutralizing capacity (ANC). Total monomeric Al concentrations explain a greater proportion of species variation than pH, suggesting that Almconcentrations may be more important in governing the distribution of chrysophyte taxa in these lakes. Gaussian logit (GL) and linear logit (LL) regressions of the relative percentages of individual chrysophyte taxa to lakewater pH and Almconcentrations and the examination of pH–Almresponse surfaces show that many chrysophyte taxa exhibit unique responses to these environmental gradients; taxa can be characterized as alkaline, circumneutral, acidic, and pH indifferent. Within each of these groups, taxa can be characterized further based upon their optima and tolerances to Almconcentrations. Chrysophyte indicator species (i.e. a taxon with a strong statistical relationship to the environmental variable of interest, a well‐defined optimum, and a narrow tolerance to the variable of interest) for pH includeMallomonas hindonii, M. crassisquama, M. pseudocoronata, andSynura uvella; M. hindonii, M. crassisquama, M. pseudocoronata, S. petersenii, andS. spinosaare good indicators of Almconcentrations. Highly significant predictive models were developed to infer lakewater pH and Almconcentrations from the relative percentages of chrysophyte scales in the study lakes. Model evaluation was based on their correlation coefficients and the root‐mean‐squared error of prediction (RMSE) derived from bootstrapping. Weighted averaging regression and calibration with tolerance down‐weighting (i.e. weighting taxa inversely to their variance) produced superior results when compared to the computationally and data‐demanding maximum likelihood methods and to simple weighted averaging regression an

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00162.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe perennially ice‐covered lakes of Antarctica have hydrodynamically stable water columns with a number of vertically distinct phytoplankton populations. We examined the photosynthesis‐irradiance characteristics of phytoplankton from four depths of Lake Bonney to determine their physiological condition relative to vertical gradients in irradiance and temperature. All populations studied showed evidence of extreme shade adaptation, including low Ikvalues (15–45 μE · m−2· s−1) and extremely low maximal photosynthetic rates (PBmless than 0.3 μg C ·μg chl a−1· h−1). Photosynthetic rates were controlled by temperature as well as light variations with depth. Lake Bonney has an inverted temperature profile within the trophogenic zone that increased from 0° C at the ice‐water interface to 6° C from 10 to 18 m. Deeper phytoplankton (10 m and 17 m) were found to have photosynthetic capacities (PBm) and efficiences (α) three to five times higher than those at the ice‐water interface. However,Q10values were only ca. 2 forPBm(no temperature dependence was evident for α), suggesting that a simple temperature response cannot explain all the differences between populations. Lake Bonney phytoplankton (primarily cryptophytes and chlorophytes) had photosynthetic characteristics similar to diatoms from other physically stable environments (e.g. sea ice, benthos) and may be ecologically analogous to mult

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00179.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe seasonal periodicity of taxa of Chrysophyceae and Synurophyceae from a small New England lake is described for the period September 1983 through June 1988. We found 51 taxa, including 29 that accounted for over 10% of the total in at least one collection. The taxa were fitted into one of five seasonal patterns. Patterns I and II represented taxa restricted to warm (pattern I) or cold (pattern II) months, respectively. Pattern HI represented organisms that began growth in the summer, persisted through autumn and disappeared with the onset of an ice cover. Pattern IV was an extension of pattern III, in which the taxon remained in the plankton throughout the winter and disappeared soon after ice out. Species without a clear seasonal pattern were grouped as pattern V. The seasonal periodicity of the flora, as examined with ordination analyses, was found to remain remarkedly similar during the 58–month study. Except for episodes of low pH during spring snow melt and unseasonally warm or cold weather, sample scores followed a fairly consistent pattern along the first and second primary axes. Water temperature, specific conductance, and pH were important variables that controlled changes in the species composition during the course of a given year. The flora was used to develop an inference model for water temperature. According to the analyses, the remains of a surface sediment sample represented a flora that grew primarily during the late autumn period at 7.6 ° C. Ways in which seasonal data could be utilized to improve paleolimnological inference work are discuss

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00186.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThe fine structure of a cyanobacterial mat collected from the fellfield ecosystems of Signy Island, Antarctica, was examined using some novel light and scanning electron microscope techniques. The mat was up to 5 mm thick and was distinctly layered. The surface of the mat consisted of nonliving material above a zone ofPhormidium autumnale(Ag.) Gom. filaments. We suggest that the surface layer protects the cyanobacterium from the effects of desiccation or high irradiance. Lower layers were less structured than the upper layer and included other taxa of cynobacteria and eukaryotic algae, although still dominated byPhormidium.The lowest layers consisted of dead organic material. The mat bound large amounts of inorganic material within and between the subsurface layers.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00199.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTMost biominerals appear to be composites of organic material and mineral. Whether biosilica is such a composite is unresolved because of a lack of evidence for such organic components. We present evidence that organic material exists within diatom biosilica and can be extracted using HF/NH4F solutions from frustules isolated fromCyclotella meneghinianaKütz and diatomaceous earth. To eliminate organic casing on the silicified frustules as a source of organic materials, the casing was removed by oxidation of frustules with NaOCl before extraction. The removal of the casing was confirmed in that oxidized frustules no longer displayed the ability to be stained with ruthenium red and fluorescamine. Frustules examined with EDXA showed an emission peak from sulfur before treatment but no peak following treatment, indicating that oxidation removed organic sulfur. The organic material obtained from extracts of fresh frustules contained both soluble and insoluble components. Only soluble material was evident in extracts from diatomaceous earth. The soluble material appears to contain glycoproteins with relatively high levels of serine and glycine. The soluble proteins from fresh frustules also appear to be phosphorylated. Indirect evidence is presented that suggests the soluble proteins may contain regions of primary structure enriched in anionic amino acids. The soluble extracts differ from general cell contents when the two fractions are compared, suggesting that frustules contain specialized organic material. The identification of silica‐specific organic material suggests that mineralization in diatoms may be in part matrix‐medi

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00202.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTThepsaBgene codes for one of two highly conserved P700 chlorophyllaapoproteins of photosystem I. This gene was cloned from the brown alga,Pylaiella littoralis(L.) Kjellm., and its primary sequence was determined. The inferred amino acid sequence of theP. littoralisprotein was compared to homologous sequences from land plants, green algae, and a cyanobacterium. ThepsaBprotein sequence is very conserved in all the examined taxa, and an unrooted phylogenetic tree, generated from a distance matrix, shows that theP. littoralisgene is closer to that of the cyanobacteriumSynechocossussp. PCC 7002 than are those of green algae, land plants, andEuglena gracilis.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00209.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY

摘要:

ABSTRACTTheGymnogongrus devoniensis(Greville) Schotter complex in the North Atlantic Ocean was elucidated by comparative molecular, morphological, and culture studies. Restriction fragment length patterns and hybridization data on organellar DNA revealed two distinct taxa in samples from Europe and eastern Canada. Nucleotide sequences for the intergenic spacer between the large and small subunit genes of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), and the adjoining regions of both genes, differed by 12.5–13.4% between the two taxa. One of the taxa, which included material from the type locality ofG. devoniensisat Torbay, Devon, England, was taken to represent authenticG. devoniensis.Within this taxon, samples from Ireland, England, northern France, northern Spain, and southern Portugal showed great morphological variation, particularly in habit, but their Rubisco spacer sequences were identical or differed by only a single nucleotide. Constant morphological features included the development, from a single auxiliary cell, of the spherical cystocarp with a thick mucilage sheath that appears to be typical ofGymnogongrusspecies with internal cystocarps. Two life‐history types were found. Northern isolates underwent a direct‐type life history, recycling apomictic females by carpospores, whereas the Portuguese isolate followed a heteromorphic life history in which carpospores gave rise to a crustose tetrasporophyte.The second group of samples, from Nova Scotia and Northern Ireland, provisionally referred to asGymnogongrussp., showed little morphological variation. The life history in both areas consists of apomictically reproducing diploid female gametophytes and diploid crustose bisporophytes and tetrasporophytes. Rubisco spacer sequences of the samples were identical, and the plasmid previously described in the Nova Scotian samples was also present in the Northern Ireland population. This species is widely distributed in the western Atlantic, from Newfoundland to Massachusetts. In Europe, gametophytes are known only at one site, but crusts are distributed from Denmark, Scotland (and probably Norway) to France. It is very likely that this species was introduced from one side of the North Atlantic to the other by shipping during the early nineteenth century. Several morphological features are unusual within the genus but are shared withG. leptophyllusJ. Agardh from the eastern Pacific Ocean, and further work is necessary to determine whetherGymnogongrussp. andG. leptophyllusare co

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1992.00214.x

出版商:Blackwell Science Inc    

年代:1992

数据来源: WILEY