Comparative studies on physiological responses to phosphorus in two phenotypes of bloom-forming Microcystis

Toxic Microcystis blooms frequently occur in eutrophic water bodies and exist in the form of colonial and unicellular cells. In order to understand the mechanism of Microcystis dominance in freshwater bodies, the physiological and biochemical responses of unicellular ( 4 strains) and colonial ( 4 strains) Microcystis strains to phosphorus ( P) were comparatively studied. The two phenotype strains exhibit physiological differences mainly in terms of their response to low P concentrations. The growth of four unicellular and one small colonial Microcystis strain was significantly inhibited at a P concentration of 0.2 mg l - 1; however, that of the large colonial Microcystis strains was not inhibited. The results of phosphate uptake experiments conducted using P- starved cells indicated that the colonial strains had a higher affinity for low levels of P. The unicellular strains consumed more P than the colonial strains. Alkaline phosphatase activity in the unicellular strains was significantly induced by low P concentrations. Under P- limited conditions, the oxygen evolution rate, Fv/ Fm, and ETRmax were lower in unicellular strains than in colonial strains. These findings may shed light on the mechanism by which colonial Microcystis strains have an advantage with regard to dominance and persistence in fluctuating P conditions.

Important aspects when modelling the interaction between surface structures and tunnelling in sand

Tunnelling in urban areas continues to increase and has highlighted the need for a better understanding of the impact of tunnel excavations on existing buildings. This paper considers the influence of surface structures on ground displacements caused by tunnelling in sand through finite element modelling and centrifuge testing. First, the importance of modelling assumptions is evaluated by comparing centrifuge modelling results to finite element modelling results for various soil constitutive models: both a Young's modulus that linearly increases with depth and a power law relation between the soil stiffness and stresses are considered. Second, the most effective soil constitutive model was used to perform a sensitivity study on the effect of different factors governing the structural response. In particular, the effect of the building stiffness and weight on the modification of soil displacements is investigated by introducing a simple surface structure. The use of a no-tension interface between the building and the soil was found to be essential to investigate the effect of weight on gap formation between the soil and the structure, as observed during the experimental tests. Results show the importance of considering the relation between the building weight and the relative stiffness between the building and the soil when assessing the structural response. © 2014 Korean Geotechnical Society.

Population growth and physiological characteristics of microalgae in a miniaturized bioreactor during space flight

A strain of microalgae (Anabaena siamensis) had been cultured in a miniaturized bioreactor during a retrievable satellite flight for 15 days. By means of remote sensing equipment installed in the satellite, we gained the growth curve of microalgae population in space every day in real time. The curve indicated that the growth of microalgae in space was slower than the control on ground. Inoculation of the retrieved microalgae culture showed that the growth rate was distinctively higher than ground control. But after several generations, both cultures indicated similar growth rates. Those data showed that algae, can adapt to space environment easily which may be valuable for designing more complex bioreactor and controlled ecological life support system in future experiment. (C) 2006 Elsevier Ltd. All rights reserved.

Physiological and biochemical microcystin-RR toxicity to the Synechococcus elongatus

Freshwater Microcystis may form dense blooms in eutrophic lakes. It is known to produce a family of related cyclic hepatopeptides (microcystins, MC) that constitute a threat to aquatic ecosystems. Most toxicological studies of microcystins have focused on aquatic animals and plants, with few examining the possible effects of microcystins on phytoplankton. In this study we chose the unicellular Synechococcus elongatus (one of the most studied and geographically most widely distributed cyanobacteria in the picoplankton) as the test material and investigated the biological parameters: growth, pigment (chlorophyll-a, phycocyanin), photosynthetic activity, nitrate reductase activity, and protein and carbohydrate content. The results revealed that microcystin-RR concentrations above 100 mug (.) L-1 significantly inhibited the growth of Synechococcus elongatus. In addition, a change in color of the toxin-treated algae (chlorosis) was observed in the experiments. Furthermore, MC-RR markedly inhibited the synthesis of the pigments chlorophyll-a and phycocyanin. A drastic reduction in photochemical efficiency of PSII (F-v/F-m) was found after a 96-h incubation. Changes in protein and carbohydrate concentrations and in nitrate reductase activity also were observed during the exposure period. This study aimed to evaluate the mechanisms of microcystin toxicity on a cyanobacterium, according to the physiological and biochemical responses of Synechococcus elongatus to different doses of microcystin-RR. The ecological role of microcystins as an allelopathic substance also is discussed in the article. (C) 2004 Wiley Periodicals, Inc.

Effects of heavy metals on plants and resistance mechanisms

Goal, Scope and Background. As one of the consequences of heavy metal pollution in soil, water and air, plants are contaminated by heavy metals in some parts of China. To understand the effects of heavy metals upon plants and the resistance mechanisms, would make it possible to use plants for cleaning and remediating heavy metal-polluted sites. Methods. The research results on the effects of heavy metals on plants and resistant mechanisms are compiled from Chinese publications from scientific journals and university journals, mostly published during the last decade. Results and Discussion. Effects of heavy metals on plants result in growth inhibition, structure damage, a decline of physiological and biochemical activities as well as of the function of plants. The effects and bioavailability of heavy metals depend on many factors, such as environmental conditions, pH, species of element, organic substances of the media and fertilization, plant species. But, there are also studies on plant resistance mechanisms to protect plants against the toxic effects of heavy metals such as combining heavy metals by proteins and expressing of detoxifying enzyme and nucleic acid, these mechanisms are integrated to protect the plants against injury by heavy metals. Conclusions. There are two aspects on the interaction of plants and heavy metals. On one hand, heavy metals show negative effects on plants. On the other hand, plants have their own resistance mechanisms against toxic effects and for detoxifying heavy metal pollution. Recommendations and Outlook. To study the effects of heavy metals on plants and mechanisms of resistance, one must select crop cultivars and/or plants for removing heavy metals from soil and water. More highly resistant plants can be selected especially for a remediation of the pollution site. The molecular mechanisms of resistance of plants to heavy metals should be studied further to develop the actual resistance of these plants to heavy metals. Understanding the bioavailability of heavy metals is advantageous for plant cultivation and phytoremediation. Decrease in the bioavailability to farmlands would reduce the accumulation of heavy metals in food. Alternatively, one could increase the bioavailability of plants to extract more heavy metals.

Effects of CO2 enrichment on the bloom-forming cyanobacterium Microcystis aeruginosa (Cyanophyceae): Physiological responses and relationships with the availability of dissolved inorganic carbon

Microcystis aeruginosa Kutz. 7820 was cultured at 350 and 700 muL.L-1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom-forming cyanobacterium. Doubling Of CO2 concentration in the airflow enhanced its growth by 52%-77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light-saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC-saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3- levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 muL.L-1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3- concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease.

EFFECTS OF LOW-TEMPERATURE AND PHYSIOLOGICAL AGE ON SUPEROXIDE-DISMUTASE IN WATER HYACINTH (EICHHORNIA-CRASSIPES SOLMS)

Superoxide dismutase activity in water hyacinth leaves was not sensitive to small changes in environmental pH, but declined markedly with greater pH changes. KCN inhibited superoxide dismutase activity, suggesting that the enzyme was mainly composed of the Cu-Zn form. Low temperature (2-degrees-C) treatment caused a decline in superoxide dismutase activity. This effect became more pronounced as the treatment time was prolonged. Furthermore, the decline was much more significant than reductions of glucose-6-phosphate dehydrogenase activity or respiration under comparable conditions. With increasing physiological age, superoxide dismutase activity declined and was significantly lower in old than in young leaves. Therefore, superoxide dismutase activity might be employed as one of physiological parameters in studying leaf senescence.

SOME ASPECTS ON INTERFACE MODES AND LO EIGENMODES IN GAAS/ALAS QUANTUM-WELLS

The interface modes and LO phonon modes in GaAs/AlAs quantum wells is investigated within the isotropic dispersionless dielectric continuum with nodes in displacement u at the interfaces as boundary condition. The interface modes are found to be purely interface polarization charge effect while LO eigenmodes induce only bulk polarization charges. Analytical expression is determined for LO eigenmodes and is found in good agreement with realistic model calculation, and its labeling index is interpreted as the helicity of electric field as it travels from one side to the other side of the slab.

New aspects of K promoted nitridation of the InP(100) surface

The effect of molecular nitrogen exposure on the InP(100) surface modified by the alkali metal K overlayer is investigated by core-level photoemission spectroscopy using synchrotron radiation. The alkali metal covered surface exhibits reasonable nitrogen uptake at room temperature, and results in the formation of a P3N5 nitride complex. Flash annealing at 400 degrees C greatly enhanced the formation of this kind of nitride complex. Above 500 degrees C, the nitride complex dissolved completely. (C) 1997 American Vacuum Society.

沙棘(Hippophae rhamnoides L.)在低温和增强UV-B胁迫下的生态生理反应

植物生长和生产力受到自然界各种形式的生物和非生物胁迫因子的影响。这些胁迫包括低温、高温、盐碱、干旱、洪水、重金属、虫害、病害和紫外线辐射等等。而人类活动大大加剧了这些胁迫所带来的影响。由于人类污染而导致臭氧层衰减以及由此产生的地球表面紫外辐射增强已经成为全球气候变化的一个主要方面。UV-B胁迫，甚至当前的辐射水平，所带来的影响已经引起科学工作者的广泛关注。 为了生存和繁殖，植物不得不面临环境中各种潜在胁迫所带来的负面影响。然而，植物生活型的不可移动性决定了其逃避胁迫的局限性。因此，绝大多数植物都是通过对胁迫作出反应，通过修复或者更新组织来降低伤害。而植物应对环境变化的能力则是由其生长模式的种属特异性和本身的遗传组成所决定。在自然界，植物常常同时面临多种胁迫，这些胁迫所引发的植物反应可能具有叠加、协同或者拮抗作用。沙棘是一种具刺、具有固氮功能的多年生雌雄异株灌木，广泛分布于亚欧大陆的温带地区和亚洲亚热带的高海拔地区。在中国，沙棘常常被用作植被恢复中的先锋树种而大量栽培。本文采用沙棘作为模式植物，试图探索木本植物对低温，UV-B辐射增强以及其与干旱的复合胁迫的响应以及沙棘对这些胁迫响应是否具有种群差异性。 对来自南北两个种群的沙棘进行短日照和低温处理，检测了其在抗寒锻炼和抗寒性发育过程中存在的性别差异。结果表明，短日照和低温都分别能够诱导抗寒锻炼的发生，而两者同时存在对所有实验植株抗寒性的大小具有叠加效应。然而，短日照和低温所诱导的抗寒性在两个种群中都具有性别差异性，雄性植株比雌雄植株对短日照和低温更为敏感。同时，南北种群间也存在差异性，北方种群的植物比南方种群的植物对短日照和低温敏感，从而在短日照下抗寒锻炼的发生时间更早，低温诱导的抗寒性更大。短日照和低温诱导植物增加抗寒性的同时伴随着脱落酸的变化。脱落酸的变化因处理，种群和性别的不同而不同。这些生理反应表明不同的沙棘种群，不同的植株性别对同一环境胁迫可能存在不同的生存策略。 比较了来自高低两个海拔的沙棘种群对于干旱和UV-B辐射增强以及两者复合胁迫条件下的生理生态反应。干旱使两个种群中植株总的生物量，总叶面积，比叶面积，叶片含碳量，含磷量，木质素含量和碳氮比显著降低，使根冠比，粗根细根比和叶片脱落酸含量显著增加。干旱而非UV-B使得δ13C 值显著增加。但是，比较而言，来自高海拔的种群对干旱反应更为强烈，而来自低海拔的种群对UV-B更敏感。在UV-B辐射增强的处理下，干旱所诱导的脱落酸的积累被显著抑制。而且我们检测到在一些指标上存在显著的干旱×UV-B交互作用，如两个种群中在总生物量上，低海拔种群中在总叶面积，粗根细根比上，高海拔种群中在比叶面积，δ13C值，木质素含量上都存在明显的交互作用。这些结果表明这两个种群对胁迫具有不同的适应性反应，来自高海拔的种群比来自低海拔的种群更能够抵御干旱和UV-B胁迫。 室外实验表明，UV-B 去除/增补对沙棘高低两个海拔种群的影响都不大。对生物量的积累，植株高度以及一些常见的胁迫反应生理指标比如丙二醛、ABA 和游离脯氨酸都没有显著影响。UV-B 的效应比UV-A 大，植物反应在无UV 和仅有UV-A 的处理间没有什么区别。然而，UV-B 去除的两个处理和UV-B 存在的两个处理间存在显著区别。UV-B 使得两个种群都显著降低了比叶面积(SLA)，但却使长期用水效率增加。但UV-B对光合色素和光合系统II 的影响不大。总体看来，来自低海拔的种群对UV-B 更为敏感。 Plant is adversely affected by various abiotic and biotic stress factors. These stressors includelow temperature, heat, salt, drought, flooding, heavy metal toxicity, wounding by herbivores,infecting by pathogenic microorganisms, ultraviolet (UV) radiation and so on. Variousanthropogenic activities have accentuated the existing stress factors. One of the mostimportant aspects of global change is that of stratospheric ozone depletion caused by seriousanthropogenic pollution and the resulting increase in UV radiation reaching the surface of theEarth. Scientists have become concerned about the effects that considerable UV-B stress, evenat current levels. In order to survive and reproduce, plants have to be able to cope with lots of potentiallyharmful stress factors that are almost constantly present in their environment. Most plants’responses under stress are to neutralize the stress, repairing the damage or regrowing newtissue rather than to avoid it due to their sessile life style. The plant defense capacity dependson plant-specific modular growth patterns and genetic make-up that allows for flexibleresponses to changing environments. Plants usually encounter several stresses simultaneouslyunder field conditions, and the stresses may cause a variety of plant responses, which can beadditive, synergistic or antagonistic. Sea buckthorn (Hippophae rhamnoides L.), a thorny nitrogen fixing deciduously perennialshrub, which is widely distributed throughout the temperate zones of Asia and Europe and thesubtropical zones of Asia at high altitudes. It has been widely used in forest restoration as thepioneer species in China. In this paper, we used sea buckthorn as a model, tried to get some understand of how plants fight low temperature, enhanced UV-B radiation level and thatcombination of drought. And also, want to know whether does there exist some populationspecific responses to such stressors. Sexual differences in cold acclimation and freezing tolerance development of two contrastingsea buckthorn (Hippophae rhamnoides L.) ecotypes from northern and southern regions inChina were recorded after exposure to short day photoperiod (SD) and low temperature (LT).The results demonstrated that cold acclimation could be triggered by exposing the plants toSD or LT alone, and that a combination of both treatments had an additive effect on freezingtolerance in all plants tested. However, development of freezing tolerance was dependent onthe sex of plants under SD and LT, the males were clearly more responsive to SD and LT thanthe females in both ecotypes studied. On the other hand, development of freezing tolerancewas also ecotype-dependent, the northern ecotype was more responsive to SD and LT than thesouthern ecotype, resulting in earlier cold acclimation under SD and higher freezing toleranceunder LT. Moreover, development of freezing tolerance induced by SD and LT wasaccompanied by changes in ABA levels. These alterations in ABA levels were different indifferent treatments, ecotypes and sexes. Therefore, the differences in SD and LT-inducedphysiological responses showed that the different ecotypes and the different sexes mightemploy different survival strategies under environmental stress. Two contrasting populations from the low and high altitudinal regions were employed toinvestigate the effects of drought, UV-B and their combination on sea buckthorn. Droughtsignificantly decreased total biomass, total leaf area, specific leaf area，leaf carbon (C),phophous (P), lignin content and the ratio of C: N in both populations, and increasedroot/shoot ratio, fine root/coarse root ratio and abscisic acid content (ABA), in bothpopulations. Drought but not UV-B resulted in significantly greater carbon isotopecomposition (δ13C) values in both populations. However, the high altitudinal population wasmore responsive to drought than the low altitudinal population. The drought-inducedenhancement of ABA in the high altitudinal population was significantly suppressed in thecombination of drought and elevated UV-B. Moreover, significant drought × UV-B interactionwas detected on total biomass in both populations, total leaf area and fine root/coarse root inthe low altitudinal population, specific leaf area, δ13C value and leaf lignin content in the high altitudinal population. These results demonstrated that there were different adaptive responsesbetween two contrasting populations, the high altitudinal population exhibited highertolerance to drought and UV-B than the low altitudinal population. A field experiment was conducted to investigate effects of UV-B exclusion/supplementationon two altitudinal populations of sea buckthorn. UV-B exclusion or supplementation had littleeffects on both populations investigated. For instance, the total biomass, plant height andsome physiological index such as Malondialdehyde (MDA), ABA and free proline were notchanged significantly. The UV-B effects are more significant than that of UV-A, nodifferences were found between treatments of excluded UV and excluded UV-B. However,compared with treatments of UV-B exclusion (including absent of UV-B and all UV band),the present of UV-B (including near ambient environment and enhanced UV-B) significantdecreased specific leaf area, and increased long time water use efficiency as evaluated by δ13Cvalue. UV-B had little effects on photosynthetic pigments and Photosystem II (PSII). The lowaltitude population is more sensitive to UV-B than that of the high altitude population.