The vertical zonation of adpressed diatoms and other epiphytic algae on Phragmites australis

The seasonal colonization and vertical zonation of adpressed and upright algae on Phragmites stems in Lake Belau, Germany, was investigated from November 1988 to October 1991. During the autumns and winters from 1988 to 1990 the dominant adpressed species included the diatoms Epithemia adnata, E. sorex, E. turgida and Rhopalodia gibba, while during the same seasons in 1990 and 1991, Cocconeis placentula var. euglypta was abundant. The upright diatoms were most abundant on the middle sections of the stems, whereas those epiphytes with most of their cell surfaces directly in contact with the substratum constituted the greatest part of the biomass on the lowest sections of the stems. Epithemia spp. and R. gibba attained their highest abundances near the sediment as well as buried beneath the most dense periphyton aggregations, while there were dense populations of C. placentula var. euglypta on the entire surface of the stems. Cocconeis is able to tolerate higher light intensities, with photosynthetically active radiation (PAR) values averaging 38?μmol?m^?2?s^?1, than Epithemia and Rhopalodia, which settle at a significantly lower PAR (26 and 20?μmol?m^?2?s^?1, respectively). The change in dominance among the adpressed species from Epithemia and Rhopalodia to Cocconeis can be explained by changes in the grazing habits of the snail Acroloxus lacustris.     

The potential effects of energy related activities on the seasonal trajectories of epiphytic marine diatoms

Seasonal successional trajectories of transplanted and experimental diatom communities were studied during the summer of 1973. Manipulation of these diatom assemblages was accomplished through the development of an in situ experimental apparatus capable of incubating these organisms without doing violence to the community itself.In one set of experiments the effects of water quality were tested on the development of inocula from grossly similar but fairly distant locations. In another set the native inoculum was incubated in the continual presence of Fe, Cu, Cr, Pb, Zn and crude oil. Seasonal succession took place in all of the control and experimental communities. During the course of succession the trajectories of assemblages under some conditions converged while others diverged. Since the random fluctuations in the environment were constant for all assemblages, the abundances of individual species were due to niche packing and interspecific restraints on the biotic potential of selected diatom species as well as the changes in water quality. The most diverse community was an experimentally mixed one. The high diversity of this community was probably due to niche packing a phenomenon which restricted the realized niches of many species and hindered their blooming. Paradoxically twice as many species (40%) had their greatest niche breadth in the mixed community as did species in the transplanted (20%) or native controls (17%). Enrichment of the incubation medium with heavy metals and oil altered the community structure and diversity of most experimental vessels. Growth of some species was depressed while that of others was enhanced. The trajectories of the communities enriched with oil and Pb were quite similar throughout the summer. The Cu and Cr assemblages initially followed the trajectory of oil and Pb but later diverged. Greatest species diversity was consistantly found in the community incubated in the presence of Cu. The Fe enriched community generally diverged from all the others. Recurrent group analysis identified distinctive groups of species for each of the experimental assemblages as well as controls.The response of these diatom communities incubated under natural conditions were characteristic of resilient communities in which populations with different structures were quickly established.Supported by ERDA Contract E (11-1) 3254, Reference Number (COO) 3254-28. The authors would like to acknowledge Dr. Howard Rubin for his assistance in writing the many computer programs used in this investigation.This paper represents a revised expansion of a thesis project accepted by the CCNY Biology Faculty in partial fulfillment of the requirements of the M.A. degree in September 1976.     

Studies on Lake Erie's littoral algae; Host specificity and temporal periodicity of epiphytic diatoms

Substratum specificity and temporal periodicity of the attached diatom flora upon three aquatic vascular plants and an artificial substratum were examined in three Lake Erie marshes. No qualitative or quantitative specificity for substrata was observed. Variability of diatom assemblage structure within replicate samples of a particular substratum type was as great as, or greater than, variability between substrata. Diatom assemblages upon dowel rod displayed a mid to late summer density maximum. Variability of density maxima upon natural substrata was attributed to different growth rates of the host macrophytes. Diatom assemblages within each sampling site possessed a distinct temporal periodicity indicating that factors affecting diatom growth are heterogeneous in distribution throughout Lake Erie's littoral zone.     

Structural characteristics of a diatom community epiphytic on Ruppia maritima

Epiphytic diatoms were collected from both the leaves and internodes of Ruppia maritima in a New Jersey salt marsh during the growing season of the host plant. Community diversity (H and the number of diatom taxa) values were initially high as Ruppia began its growth, but quickly dropped to sustained low levels as vegetative growth of the host ceased and new attachment sites were no longer available. A critical examination of all structural characteristics indicated that the leaves and internodes of Ruppia support a single, nearly homogeneous epiphytic diatom community. An analysis of variance indicated that differences between leaves and internodes were minimal, as did a comparison of the assemblages present on these two sites by a selected similarity index. A total of 57 taxa were encountered and the single dominant taxon was Navicula pavillardi, which accounted for one out of every three individuals counted. A comparison of the epiphytic diatom community with those inhabiting the sediments on the marsh proper revealed that the marsh sediments were the major source of individuals for Ruppia colonization.     

New tools for labeling silica in living diatoms

Silicon biomineralization is a widespread mechanism found in several kingdoms that concerns both unicellular and multicellular organisms. As a result of genomic and molecular tools, diatoms have emerged as a good model for biomineralization studies and have provided most of the current knowledge on this process. However, the number of techniques available to study its dynamics at the cellular level is still rather limited. Here, new probes were developed specifically to label the pre-existing or the newly synthesized silica frustule of several diatoms species. It is shown that the LysoTracker Yellow HCK-123, which can be used to visualize silica frustules with common filter sets, presents an enhanced signal-to-noise ratio and allows details of the frustules to be imaged without of the use of ionophores. It is also demonstrated that methoxysilane derivatives can be coupled to fluorescein-5-isothiocyanate (FITC) to preferentially label the silica components of living cells. The coupling of labeling procedures might help to address the challenging question of the process of frustule exocytosis.     

Impacts of cultivation of marine diatoms on the associated bacterial community

The composition of bacterial communities associated with four diatom species was monitored during isolation and cultivation of algal cells. Strong shifts in the associated communities, linked with an increase in the numbers of phylotypes belonging to members of the Gammaproteobacteria, were observed during cultivation.     

Stream epilithic, epipelic and epiphytic diatoms: habitat fidelity and use in biomonitoring

We compared the use of epilithic, epiphytic, and epipelic diatom communities in stream biomonitoring by investigating species composition and relationships with measured water quality variables in two tributaries of the Grand River, Ontario, Canada. Although ordination showed some separation of the epilithon from other habitats, clear habitat preferences and seasonality were not identified. Canonical correspondence analysis showed that measured water quality variables explained the major gradients in the diatom data for all three habitats. The diatoms from each habitat were strongly related to alkalinity, suspended solids, biological oxygen demand and conductivity, and in addition, epipelic and epiphytic diatoms showed significant relationships with total phosphorus. It was concluded that although some species were more abundant in one habitat than the others, the community structure of the epilithic, epiphytic and epipelic habitats from these streams was not consistently different. The results indicate no apparent benefit to sampling discrete habitats for water quality monitoring using diatoms, however, the best relationship are obtained using the sum of the diatom data from all three habitats.     

The structure of diversity in an epiphytic chironomid community

The structure of diversity in a chironomid community inhabiting submerged macrophytes was analysed, including the relationship between predation/competition and chironomid diversity. Diversity as expressed by the Shannon functionH was found to be strongly associated with equitabilityJ but not with species richnessS in this community. Chironomid species richness was correlated with the abundance of diatoms. DiversityH and equitabilityJ were significantly correlated with chironomid density through the year. Invertebrate predators were generally rare and occurred sporadically throughout the year in this habitat, with only three species (Chaetogaster diaphanus, Rhyacophila dorsalis andZavrelimyia sp.) attaining >25% habitat occupancy. Neither these predators nor non-chironomid competitors encountered in the same habitat (Stylaria lacustris, Ophidonais serpentina, Hydroptila sp.,Simulium spp. andHydropsyche siltalai) appeared to affect diversity measures of the chironomid community under study, apart from a weak tendency of highSimulium density negatively affecting the total chironomid abundance. In conjunction with other analyses, this chironomid community seemed to be stochastically dynamic and was little influenced by biotic factors such as predation and competition.     

Geographical and seasonal patterns of epiphytic diatoms on a subtropical mangrove (Kandelia candel) in southern China

Geographical and seasonal patterns of epiphytic diatoms on a subtropical mangrove (Kandelia candel (L.) Druce) were examined at four sites in southern China. A total of one hundred and three epiphytic diatom species and varieties belonging to 40 genera were identified. Dominant species included Nitzschia fasciculata, Luticola mutica and Achnanthes javanica var. subcontricta. Further analysis using canonical correspondence analysis revealed three diatom associations which could be closely related to environmental variables such as salinity and nutrients resources of nitrogen and phosphate. Epiphytic diatom assemblages on roots would be a good indicator for the evaluation of water quality in mangroves.     

沉水植物附着细菌群落结构及其多样性研究进展

与陆生植物类似,沉水植物的叶表也存在着大量的附着细菌。附着细菌拥有独特的生态位和显著的生态功能,与沉水植物构成了复杂的共生体系。针对附着细菌的群落结构及其多样性进行了简单的综述。在方法学上,"表面活性剂+超声处理"的方式能够比较有效地洗脱叶表的附着细菌。显微计数和分离培养的方法分别发现,某些沉水植物附着细菌的多度在105~107个/cm2以及106 CFU/cm左右。克隆测序的研究表明沉水植物附着细菌的OTU在几十到上百的范围内。在群落结构上,Betaproteobacteria、Bacteroidetes、Alphaproteobacteria、Actinobacteria、Planctomycetes、Cyanobacteria等门类的细菌较为常见。先锋物种在附着细菌生物膜的形成过程中发挥着关键作用,环境条件和植物体都会对附着细菌的多样性造成影响。富营养化水体观察到较高的附着细菌丰度,溶解性有机物比无机营养物更加适合附着细菌的利用。植物体的叶片化学组成、渗出物以及物理结构等会影响附着细菌的多样性及群落结构。对沉水植物附着细菌群落结构形成的机理进行了假说性质的总结,并对附着细菌的研究前沿进行了展望。     

Influence of currents and waves on the whirling up of benthic diatoms living on intertidal flats

Summary Experimental observations showed that the presence of relatively dense populations of benthic diatoms in the water can be caused by water currents of relatively low velocity. However, field observations showed that wave action can strongly increase the whirling up of these populations. Observations done in the laboratory and in the field showed that benthic diatoms reached the water column together with resuspended sediment. The field observations indicated that, in contrast with the fine sediment fraction, bare parts of sand grain particles are relatively insignificant as a substrate for benthic diatoms. It is suggested that in turbid areas with extensive flats the benthic diatom populations are an important additional food source for the pelagic fauna.Publication no. 47 of Biological Research Ems-Dollard Estuary.     

Effects of light intensity on the epiphytic bacterial community of sporelings of Saccharina japonica

Journal of Applied Phycology - In the artificial hatchery of Saccharina japonica, sporelings suffer from various diseases caused by improper irradiance. On the other hand, the outbreaks of diseases...     

A novel method for low load friction testing on living cells

A low load tribology technique for studying the effects of friction on living cells was developed. Results show a direct relationship between the coefficient of friction (COF) and the extent of cell damage. The COF, μ, for a glass pin on an intact layer of human corneal epithelial cells is determined to be on the order of μ = 0.05 ± 0.02 (n = 16). The correlations between applied normal load and extent of cell damage, as well as between number of reciprocation cycles and cell damage, are reported. It is also found that cell damage can occur when a loading force as low as 0.5 mN is applied, although the cells appear to be intact.     

Randomness and aggregation: analysis of dispersion in an epiphytic chironomid community

1. Patterns of dispersion in a chironomid community on the submersed macrophyte Myriophyllum spicatum were analysed. 2. Random dispersion commonly occurred throughout the year, with an average of 40% of all species being observed with random spatial patterns. The frequency of occasions with random dispersion varied among chironomid species, ranging from 3.3% in Rheotanytarsus curtistylus to 56% in Thienemanniella majuscula. 3. Estimates of the negative binomial parameter k show that 26% of all cases demonstrate strong aggregation (0 < k < 1.0) while nearly half (47%) have quasi-random dispersion. Interspecific variation in k was not significant statistically when all the species were considered together, although a pairwise comparison between two abundant species Tvetenia calvescens and Rheotanytarsus curtistylus demonstrated a marginally significant difference. When different instars were compared, the percentage frequency of strong aggregation (0 < k < 1.0) declined from first instars (49%) to later instars (II-38%, III-24% and IV-27%). 4. Variance/mean and m*—m regressions (m* is Lloyd's mean crowding statistic and m is the sample mean) both fitted the data well, but there was little indication of significant interspecific variation in parameter values, particularly the slope of regression. 5. Dispersion patterns were examined along with the analysis of spatial overlap in this community. Forty-two per cent of species-pairs with reduced spatial overlap (spatially ‘segregated’ pairs) contained one or both species with random dispersion, while the corresponding value for spatially unsegregated pairs was 57%. This suggests that spatial segregation is not necessarily caused by strong, independent aggregation of both species. Comparing spatially segregated vs. unsegregated pairs, the former tend to have one species with a stronger tendency of aggregation than species of the latter. 6. Patterns of dispersion observed were considered in the light of ‘random patch formation’. Random patch formation emphasizes the stochasticity of patch-forming processes as well as the stochastically dynamic nature of resultant patches. Unlike terrestrial drosophilid assemblages, where strong aggregation is a predominant pattern, this chironomid community demonstrates widely varying degrees of dispersion with high occurrence of randomness, reflecting the stochasticity of dispersal and recolonization processes. It is suggested that, in terms of species coexistence, more emphasis should be placed on stochasticity rather than on aggregation in this type of community.     

Purification of biosilica from living diatoms by a two-step acid cleaning and baking method

Due to their sustainability, intact cell walls, availability of pure cultures, and others, living diatoms show a lot of promise for the application in various fields in particular for micro/nano-devices. In order to purify the biosilica structures of diatoms called frustules, a two-step acid cleaning and baking method was employed. By this path, organic matter and inorganic impurities can be removed very effectively. In addition, the highest quality of frustules was achieved when the samples were cleaned in an excess of boiling 10~15 % HCl and subsequently heated to 600 °C at a heating rate of 3 °C min^?1 for 6 h. In our operation, the native frustule morphology was maintained completely, and dry frustules with more than 90 % SiO₂ in weight can be obtained, and furthermore, the surface area of them reached a good value of 48.47 m² g^?1.     

High diversity and low specificity of fungi associated with seedless epiphytic plants

Epiphytes, which grow on other plants for support, make up a large portion of Earth's plant diversity. Like other plants, their surfaces and interiors are colonized by diverse assemblages of fungi that can benefit their hosts by increasing tolerance for abiotic stressors and resistance to disease or harm them as pathogens. Fungal communities associated with epiphytic plants and the processes that structure these communities are poorly known. To address this, we sampled seven epiphytic seedless plant taxa in a Costa Rican rainforest and examined the effects of host identity and microhabitat on external and endophytic fungal communities. We found low host specificity for both external and endophytic fungi and weak differentiation between epiphytic and neighboring epilithic plant hosts. High turnover in fungi within and between hosts and habitats reveals that epiphytic plant-associated fungal communities are highly diverse and suggests that they are structured by stochastic processes.     

Effects of ultraviolet–B irradiances on soybean

Soybean [Glycine max (L.) Merr. cv. Hardee] and wheat (Triticum aestivum L. cv. Jori) were grown from seed under four ultraviolet-B irradiances and four levels of photosynthetically active radiation in a factorial design. The effects of ultraviolet-B radiation on leaf number and area, total dry matter production, dry weight of component organs, and plant height were compared between soybean and wheat. Ultraviolet-B radiation effects were dependent upon the level of photosynthetically active radiation incident during growth. Wheat and soybeans were both affected by low ultraviolet-B radiation flux densities; however, they differed markedly in their growth responses and biomass allocation patterns. Substantial interactions between ultraviolet-B and photosynthetically active radiation indicate a need for the measurement of longer wavelength radiation when evaluating the effects of ultraviolet-B radiation on plant growth in natural conditions.