Biomass, species composition and diversity of epipelic algae in mire pools

The biomass, species composition and diversity of epipelic algae in two small pools of contrasting physicochemical characteristics in Miyatoko Mire were studied in 1992 (pool 3 =site B4 and pool 50 =site D2). A total of 93 species and 67 species of epipelic algae occurred at sites B4 and D2, respectively. Considerable differences were observed between the two sites in the seasonal fluctuations of species number, biomass and dominant species. At site B4, little changed with species number during April–August and markedly increased in October, while biomass was largest in April and gradually decreased during June–October. Diatoms and desmids occupied 33–82% and 15–63% of total algal biomass, respectively. At site D2, species number and biomass were small in April just after the snow-thaw, and increased in June and decreased in August and October. Diatoms occupied 90–98% of total algal biomass. The species diversity was always higher at site D2 than B4. As a result of analyses of water chemistry in the two pools, pool B4 can be recognized as a habitat experiencing high disturbance frequency. It is predicted that pools experiencing frequent disturbance will have less epipelic algal biomass and diversity.     

Effects of UV-B radiation on growth and motility of four phytoplankton species

A depletion of the stratospheric ozone layer would result in an increased UV-B radiation, which could have harmful effects on marine organisms. The aim of this study was to determine the effects of an enhanced UV-B radiation (280–320 nin) on the motility and growth in four Swedish phytoplanklon species. The different plankton species were exposed to different doses of UV-B radiation during growth. The growth of the motile dinoflagellates, Gyronidium aureolum Hulburt (Ba 6), and Prorocentrum minimum (Pav.) P. Schiller (Ba 12), was more sensitive to UV-B radiation than the non-motile diatoms Dityhim brightwellii (P. West) Grun (Ba 15) and Phaeodactylum tricornutum Bohlin (Ba 16). One week of UV-B radiation 2 h daily (159 J m⁻² day⁻¹), had a dramatic effect on the growth of the dinoflagellates, while the diatoms were nearly unaffected. On the other hand, when given higher intensity of UV-B radiation (312, 468 and 624 J m⁻² day⁻¹) during the initial phase of growth, also the growth of the diatom, D. brightwellii, was inhibited. Not only the growth but also the swimming speed of the dinoflagellates C. aureolum and P. minimum were affected by UV-B radiation. The speed decreased rapidly after 1–2 h of UV-B radiation (312 J m⁻² day⁻¹), and after longer irradiation times the dinoflagellates lost their motility. G. aureolum exposed to UV-B radiation, regained normal speed after two weeks of visible light.     

The response of the early developmental stages of Laminaria japonica to enhanced ultraviolet-B radiation

The responses of the early development of Laminaria japonica collected from Kiaochow Bay in China to enhanced ultraviolet-B radiation (UV-B, 280—320 nm) were studied in the laboratory. The low UV-B ra-diations (11.7—23.4 J·m-2·d-1) had no significant effects on zoospores attachment, but when the UV-B dose > 35.1 J·m-2·d-1 the attachment decreased significantly compared with the control. Germination of embryospores was >93% under the low (11.7—35.1 J·m-2·d-1) doses, and in the range of 78.5%—88.5% under the high (46.8—70.2 J·m-2·d-1) UV-B doses, indicating a significant radiation effect. Under the higher UV-B exposure (35.1—70.2 J·m-2·d-1), all of the few gametophytes formed from embryospores died 120 h post-release. After exposure to the low UV-B radiation (11.7—23.4 J·m-2·d-1), the formation of sporophytes decreased and the female gametophyte clones increased compared with the control. However, the sex ratio and the relative growth of female gametophytes/sporophytes had not signifi-cantly changed. According to the results, enhanced UV-B radiation has a significant effect on the early development of L. japonica under laboratory conditions, suggesting that the UV-B radiation could not be overlooked as one of the important environmental factors influencing the ontogeny of macroalgae living in marine ecosystems.     

Moisture availability influences the effect of ultraviolet-B radiation on leaf litter decomposition

Altered surface ultraviolet‐B (UV‐B) radiation resulting from a combination of factors that include changes in stratospheric ozone concentrations, cloud cover, and aerosol conditions may affect litter decomposition and, thus, terrestrial nutrient cycling on a global scale. Although litter decomposition rates vary across biomes, patterns of decomposition suggest that UV‐B radiation accelerates litter decay in xeric environments where precipitation is infrequent. However, under more frequent precipitation regimes where litter decay rates are characteristically high, the effect of UV‐B radiation on litter decomposition has not been fully elucidated. To evaluate this association between moisture regime and UV‐B exposure, a litter decomposition experiment was designed for aspen (Populus tremuloides) leaf litter, where conditions that influence both abiotic (photodegradation) and biotic (microbial) processes could be manipulated quantitatively. We found that experimentally increasing UV‐B exposure (0, 7.4, and 11.2 kJ m^?2 day^?1, respectively) did not consistently increase litter decomposition rates across simulated precipitation frequencies of 4, 12, and 24 days. Instead, a UV‐B exposure of 11.2 kJ m^?2 day^?1 resulted in a 13% decrease in decomposition rates under the 4‐day precipitation frequency, but an increase of 80% under the 24‐day frequency. Furthermore, the same UV‐B dose increased litter decomposition rates under the 24‐day precipitation frequency by 78% even in conditions where microbial activity was suppressed. Therefore, under more xeric conditions, greater exposure to UV‐B radiation increased decomposition rates, presumably through photodegradation. In contrast, when decomposition was not moisture‐limited, greater UV‐B exposure slowed decomposition rates, most likely from the resulting inhibition of microbial activity. Ultimately, these experimental results highlight UV‐B radiation as a potential driver of decomposition, as well as indicate that both the direction and magnitude of the UV‐B effect is dependent on moisture availability, a factor that may change according to future patterns in global precipitation.     

Patterns in freshwater diatom taxonomic distinctness along an eutrophication gradient

1. A variety of species richness measures have been used to assess the effects of environmental degradation on biodiversity. Such measures can be highly influenced by sample size, sampling effort, habitat type or complexity, however, and typically do not show monotonic responses to human impact. In addition to being independent of the degree of sampling effort involved in data acquisition, effective measures of biodiversity should reflect the degree of taxonomical relatedness among species within ecological assemblages and provide a basis for understanding observed diversity for a particular habitat type. Taxonomic diversity or distinctness indices emphasize the average taxonomic relatedness (i.e. degree of taxonomical closeness) between species in a community. 2. Eutrophication of freshwater ecosystems, mainly due to the increased availability of nutrients, notably phosphorus, has become a major environmental problem. Two measures of taxonomic distinctness (Average Taxonomic Distinctness and Variation in Taxonomic Distinctness) were applied to surface sediment diatoms from 45 lakes across the island of Ireland to examine whether taxonomic distinctness and nutrient enrichment were significantly related at a regional scale. The lakes span a range of concentrations of epilimnic total phosphorus (TP) and were grouped into six different types, based on depth and alkalinity levels, and three different categories according to trophic state (ultra‐oligotrophic and oligotrophic; mesotrophic; and eutrophic and hyper‐eutrophic). 3. The taxonomic distinctness measures revealed significant differences among lakes in the three different classes of trophic state, with nutrient‐rich lakes generally more taxonomically diverse than nutrient‐poor lakes. This implies that enrichment of oligotrophic lakes does not necessarily lead to a reduction in taxonomic diversity, at least as expressed by the indices used here. Furthermore, taxonomic distinctness was highly variable across the six different lake types regardless of nutrient level. 4. Results indicate that habitat availability and physical structure within the study lakes also exert a strong influence on the pattern of taxonomic diversity. Overall the results highlight problems with the use of taxonomic diversity measures for detecting impacts of freshwater eutrophication based on diatom assemblages.     

Role of ultraviolet-B radiation on bacterioplankton and the availability of dissolved organic matter

Attenuation of ultraviolet (UV)-radiation into the water column is highly correlated with the concentration of the dissolved organic matter (DOM). Thus UV penetrates deeper into marine waters than into freshwater systems. DOM is efficiently cleaved by solar surface radiation levels consuming more oxygen than bacterial metabolism. This photolytically cleaved DOM exhibits higher absorbance ratios (250/365 nm) than untreated DOM. Natural bacterioplankton reach higher abundance if inoculated in previously solar-exposed DOM than in untreated DOM; during bacterial growth the absorbance ratio declines steadily indicating the utilization of the photolytically cleaved DOM. On the other hand, bacterioplankton are greatly reduced in their activity if exposed to surface solar radiation levels. Photoenzymatic repair of DNA induced by UV-A radiation, however, leads to an efficient recovery of bacterial activity once the UV-B stress is released. Turbulent mixing of the upper layers of the water column leads to a continuous alteration of the UV exposure regime. Close to the surface, bacteria and DOM are exposed to high levels of UV-B leading to a reduction in bacterial activity and to photolysis of DOM. Once mixed into deeper layers where UV-B is attenuated, but sufficient UV-A is remaining to allow photoenzymatic repair, the photolytically cleaved DOM is efficiently taken up by bacterioplankton leading to even higher bacterial activity than prior to the exposure. Thus, the overall effect of UV on bacterioplankton is actually an enhancement of bacterial activity despite their lack of protective pigments.     

The lipid composition of the non-photosynthetic diatom Nitzschia alba

The lipid composition of the non-photosynthetic marine diatom, Nitzschia alba, has been quantitatively determined. Triglycerides accounted for 20% of the cell dry weight and 87% of the total lipids. Smaller amounts of 1,2- and 1,3-diglycerides, free sterol (24-methylene cholesterol), hydrocarbons and an unknown component were the remaining neutral lipids detected. Phosphatidylsulfocholine (phosphatidyl S,S-dimethylmercaptoethanol), present in amounts of 0.8% of cell dry weight (35% of total polar lipids), was the major polar lipid component. Other phospholipids were lysophosphatidylsulfocholine, phosphatidylglycerol, phosphatidylinositol and cardiolipin, but both phosphatidylcholine and phosphatidylethanolamine were completely absent. Another novel sulfolipid, deoxyceramide sulfonic acid, as well as the sulfate ester of the free sterol, were also present. Considerable amounts of the four lipids often associated with photosynthetic organisms, mono- and di-galactosyl diglycerides, sulfoquinovosyl diglyceride and phosphatidylglycerol, were identified in N. alba. However, the fatty acid components of the glycosyl diglycerides did not show the high amounts of polyunsaturated acids (18 : 2, 18 : 3) normally found in photosynthesizing organisms. All polar lipids were found to be associated with various cell membrane fractions in N. alba.     

Sperm structure and motility of the freshwater teleost Cottus gobio

When motility of spermatozoa of Cottos gobio was initiated with distilled water, the motility rate decreased to 0% within 1 min, and significant signs of osmotic alterations were observed at the end of the motility period. By contrast, in 50 mmol 1⁻¹ NaCl solution, the motility rate persisted for 120–140 min. In both distilled water and in 50 mmol 1⁻¹ NaCl solution, the main swimming type of spermatozoa was linear motion during the whole motility period. The initial swimming velocity (50.0 ± 2.1 μm s⁻¹) measured 10 s after motility initiation was similar in both distilled water and in 50 mmol 1⁻¹ NaCl solution. In distilled water, the velocity decreased to <20 μm s⁻¹ (locally motile) during the first minute of the motility phase. In 50 mmol 1⁻¹ NaCl solutions, it remained at a constant level during the first 60 min of the motility period, but then started to decrease to <20 μm s⁻¹ after 120 min. When 5 mmol 1⁻¹ potassium cyanide, antimycin or atractyloside was added to the 50 mmol 1⁻¹ NaCl solution, the motility period was reduced to ≤2min. Ten millimoles per litre 2-deoxy-D-glucose, malonate or a mixture of 5 mmol 1⁻¹ atractyloside and 5 mmol 1⁻¹ carnithine did not effect the duration of the motility period. This indicates that sperm energy metabolism depends mainly on respiration rate and fatty acid metabolism.     

The response of the early developmental stages of Laminaria japonica to enhanced ultraviolet-B radiation

The responses of the early development of Laminaria japonica collected from Kiaochow Bay in China to enhanced ultraviolet-B radiation (UV-B, 280–320 nm) were studied in the laboratory. The low UV-B radiations (11.7–23.4 J·m⁻²·d⁻¹) had no significant effects on zoospores attachment, but when the UV-B dose > 35.1 J·m⁻²·d⁻¹ the attachment decreased significantly compared with the control. Germination of embryospores was >93% under the low (11.7–35.1 J·m⁻²·d⁻¹) doses, and in the range of 78.5%–88.5% under the high (46.8–70.2 J·m⁻²·d⁻¹) UV-B doses, indicating a significant radiation effect. Under the higher UV-B exposure (35.1–70.2 J·m⁻²·d⁻¹), all of the few gametophytes formed from embryospores died 120 h post-release. After exposure to the low UV-B radiation (11.7–23.4 J·m⁻²·d⁻¹), the formation of sporophytes decreased and the female gametophyte clones increased compared with the control. However, the sex ratio and the relative growth of female gametophytes/sporophytes had not significantly changed. According to the results, enhanced UV-B radiation has a significant effect on the early development of L. japonica under laboratory conditions, suggesting that the UV-B radiation could not be overlooked as one of the important environmental factors influencing the ontogeny of macroalgae living in marine ecosystems. Supported by the Program for New Century Excellent Talents in University (Grant No. NCET-05-0597) and National Natural Science Foundation of China (Grant No. 30270258)     

The influence of present-day levels of ultraviolet-B radiation on seedlings of two Southern Hemisphere temperate tree species

Seedlings of two Southern Hemisphere temperate trees species (mountain beech: Nothofagus solandri var. cliffortioides (Hook. f.) Poole and broadleaf: Griselinia littoralis Raoul) were grown in the field to determine the effects of present-day levels of ultraviolet-B radiation (UV-B) on growth, biomass, UV-B absorbing compounds, leaf optical properties and photoinhibition. Plants were covered with either UV-B transmitting or UV-B absorbing filters. After 125 days of typical summer weather, total biomass of both species was not affected by the UV-B treatments. Without UV-B, height increased (23%) and the number of leaves produced decreased (–21%) in beech, but broadleaf was unaffected. The effect of UV-B on beech height and leaf number was manifest during a second flush of leaves suggesting differences in response to UV-B of leaves initiated in different seasons and UV-B radiation regimes. Leaves of both species were essentially opaque to the transmission of UV-B. In the absence of UV-B the transmission of photosynthetically active radiation through leaves of both species increased, foliar nitrogen concentrations increased and levels of UV-B absorbing compounds decreased. In the youngest leaves of beech but not of broadleaf, removal of UV-B reduced midday photoinhibition, and did not alter the complete recovery of the fluorescence ratio F_V/F_M in the evening to predawn levels. As leaves of both species aged, midday photoinhibition decreased, with the result that UV-B had no effect on photoinhibition in mature leaves. Results of this experiment show that even under present-day UV-B levels, UV-B radiation modifies the physiology, optical properties and secondary compounds of leaves of both beech and broadleaf seedlings.     

The effects of solar ultraviolet-B radiation on the growth and yield of barley are accompanied by increased DNA damage and antioxidant responses

There is limited information on the impacts of present-day solar ultraviolet-B radiation (UV-B) on biomass and grain yield of field crops and on the mechanisms that confer tolerance to UV-B radiation under field conditions. We investigated the effects of solar UV-B on aspects of the biochemistry, growth and yield of barley crops using replicated field plots and two barley strains, a catalase (CAT)-deficient mutant (RPr 79/4) and its wild-type mother line (Maris Mink). Solar UV-B reduced biomass accumulation and grain yield in both strains. The effects on crop biomass accumulation tended to be more severe in RPr 79/4 (≈ 32% reduction) than in the mother line (≈ 20% reduction). Solar UV-B caused measurable DNA damage in leaf tissue, in spite of inducing a significant increase in UV-absorbing sunscreens in the two lines. Maris Mink responded to solar UV-B with increased CAT and ascorbate peroxidase (APx) activity. No effects of UV-B on total superoxide dismutase (SOD) activity were detected. Compared with the wild type, RPr 79/4 had lower CAT activity, as expected, but higher APx activity. Neither of these activities increased in response to UV-B in RPr 79/4. These results suggest that growth inhibition by solar UV-B involves DNA damage and oxidative stress, and that constitutive and UV-B-induced antioxidant capacity may play an important role in UV-B tolerance.     

The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradient

Aim To interpret the unimodal relationship between diatom species richness and lake pH within the context of the evolutionary species pool hypothesis (SPH). We test the following primary prediction arising from the SPH: the size of the potential species pool (PSP) will increase along a gradient representing the historical commonness of different pH environments (pH commonness). To do this we assume that the present‐day spatial dominance of near‐neutral pH conditions compared with acidic and alkaline conditions reliably mimics the relative spatial availabilities of historical pH conditions among freshwater lakes. We also determine whether local richness represents a constant proportion of PSP size along the pH commonness gradient. Location Two hundred and thirty‐four lakes distributed over a 405,000 km² region of the north‐eastern United States of America. Methods Sediment diatom morphospecies lists and pH data were acquired from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) website. Using 248 morphospecies that occurred in at least 10 of the 234 lakes, four different measures of PSPs were calculated along the pH gradient. Local species richness was equated with the number of species occurring within the lake. Alpha diversity was equated with the average species richness of lakes with similar pH values. A combination of statistical methods were employed, including correlations, quadratic regression and piecewise regression. Results PSP size increased significantly with pH commonness for all four measures of PSP size, thus supporting the primary prediction of the evolutionary SPH. Local richness comprised a larger proportion of the PSP within acidic lakes than within circumneutral lakes. Alpha diversity and lake species richness both increased significantly with pH commonness, but the former did so in a two‐step fashion. We test and reject several alternative contemporary time‐scale explanations for our findings. Main Conclusions Our findings are consistent with the hypothesis that diatom taxonomic richness is presently lower within acidic and highly alkaline lakes than in circumneutral lakes owing to the limited opportunity in space and/or time for the evolution of suitably adapted species. Whereas ecological processes can explain why certain species are excluded from particular habitats, e.g. acidic lakes, they cannot account for why so few species are adapted to those habitats in the first place.     

Two new species of Nitzschia (Bacillariophyceae) from freshwater environs of Lonar Crater Lake,India

Diatom taxa in India were first documented by Ehrenberg and subsequently many studies have focused on the Western Ghats and Himalayan mountains while other regional environments were rarely explored. In the current study, the freshwater environs of the saline Lonar Crater Lake were investigated and two new Nitzschia species have been described. Nitzschia kociolekii sp. nov. and Nitzschia tripudio sp. nov. were sampled from bird feeding ponds associated with Lonar Lake. The morphological characters of the new species are similar to N. amphibia and N. frustulum but differ in terms of striae pattern, polymorphic areolae development, fibula and stria density. In addition, larger specimens of N. williamsii, a recently described taxon from Bangalore wetlands of Peninsular India, were found in a waterfalls flowing into Lonar Lake. All three taxa are freshwater diatoms and are possibly endemic to Peninsular India.     

Effects of methylmercury and inorganic mercury on periphytic diatom communities in freshwater indoor microcosms

The effects of inorganic mercury (HgII) and methylmercury (MeHg) on the colonization of artificial substrates by periphytic diatoms were studied using indoor freshwater microcosms. These consisted of a mixed biotope– water column + natural sediment – with rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea).The periphyton was collected on glass slides in the water column after 34and 71 days. The two Hg sources were introduced either by daily additions to the water column, or once at the beginning into the sediment, using two nominal concentrations: water column, 0.5 μgL^-1 and 2 μg L^-1 for both compounds: sediment, 0.5 mg kg^-1 (fw) and 2 mgkg^-1 (fw) for MeHg and 1 mg kg^-1 (fw) and 10 mgkg^-1 (fw) for HgII. Several complementary criteria were used to analyse the structural and functional perturbations induced: cell density, species richness, diatom size, relative abundance. Exposure to MeHg added to the water column resulted in reduced cell density and changes in species composition with enhancement of e.g. Fallacia pygmaea or Nitzschia palea; inorganic Hg had less effect on the population structure. After contamination via the sediment, the effects of the two compounds were less pronounced than for the water source. This revised version was published online in August 2006 with corrections to the Cover Date.     

The effect of land use on the diatom communities in lakes

Data on recenr diatom community structure and relevant environmental characteristics from the lakes and their catchments have been collected from 151 oligotrophic lakes in eastern Finland. The pattern of frequency distribution of diatoms as a function of environmental variables, including land use in the catchment, differs between diatom taxa and indicates the optimum conditions and amplitude of occurrence for particular species. This kind of study should lead to increased understanding of the environmental requirements of diatom species and will be useful in the interpretation of historical changes in lakes as well as in forecasting possible future changes.     

Differential effects of elevated ultraviolet-B radiation on plant species of a dune grassland ecosystem

In a greenhouse study, plants of three monocotyledonous and five dicotyledonous species, which occur in a Dutch dune grassland, were exposed to four levels of ultraviolet-B (UV-B) radiation. UV-B levels simulated up to 30% reduction of the stratospheric ozone column during summertime in The Netherlands. Six of the plant species studied in the greenhouse were also exposed to enhanced UV-B irradiance in an experimental field study. In the field experiment plants either received the ambient UV-B irradiance (control) or an enhanced UV-B level simulating 15–20% ozone depletion during summertime in The Netherlands. The purpose of both experiments was to determine the response of the plant species to UV-B radiation and to compare results obtained in the greenhouse with results of the field experiment. Large intraspecific differences in UV-B sensitivity were observed in the greenhouse study. Total dry matter accumulation of monocotyledons was increased, while dry matter accumulation of dicotyledons remained unaffected or decreased. The increase in biomass production of monocotyledons at elevated UV-B was not related to the rate of photosynthesis but to alterations in leaf orientation. In the greenhouse study, UV-B radiation also affected morphological characteristics. Shoot height or maximum leaf length of five out of eight species was reduced. In the field study only one species showed a significantly decreased maximum leaf length at enhanced UV-B. Possible reasons for this discrepancy are discussed. The absorbance of methanolic leaf extracts also differed between species. UV absorbance of field-grown plants was higher than greenhouse-grown plants. In the greenhouse study, the highest UV-B level increased UV-B absorbance of some species. In the field study however, this stimulation of UV absorbance was not observed. In general, results obtained in the greenhouse study were similar to results obtained in the field study. Difficulties in extrapolating results of UV-B experiments conducted in the greenhouse to the field situation are discussed.     

滤减UV B辐射对烟叶可溶性蛋白、〖HJ*3〗〖HJ*2〗光合色素和类黄酮的影响

在云南玉溪烟区种植烤烟海拔最高(1806.0m)的通海县,通过盆栽烤烟K326试验,研究了在滤减自然的太阳UV-B辐射强度25%、50%和65%条件下,UV-B辐射对烟叶发育过程中可溶性蛋白、光合色素和类黄酮的影响。结果表明:随叶龄增加,可溶性蛋白含量下降,光合色素降解,类黄酮在老叶中积累,蛋白质在生理成熟期对UV-B辐射最敏感。与对照相比,减弱UV-B辐射处理降低了烟叶类黄酮和可溶性蛋白含量,但光合色素含量上升;较低的UV-B辐射降低了叶绿素的降解速度。结果从一侧面说明UV-B辐射对烟叶蛋白质的合成是有益的,类黄酮和叶绿素的变化是对UV-B辐射变化的适应性反应,类黄酮与蛋白质之间可能存在一定的偶联关系。