Optimal nitrogen-to-phosphorus stoichiometry of phytoplankton

Redfield noted the similarity between the average nitrogen-to-phosphorus ratio in plankton (N:P = 16 by atoms) and in deep oceanic waters (N:P = 15; refs 1, 2). He argued that this was neither a coincidence, nor the result of the plankton adapting to the oceanic stoichiometry, but rather that phytoplankton adjust the N:P stoichiometry of the ocean to meet their requirements through nitrogen fixation, an idea supported by recent modelling studies. But what determines the N:P requirements of phytoplankton? Here we use a stoichiometrically explicit model of phytoplankton physiology and resource competition to derive from first principles the optimal phytoplankton stoichiometry under diverse ecological scenarios. Competitive equilibrium favours greater allocation to P-poor resource-acquisition machinery and therefore a higher N:P ratio; exponential growth favours greater allocation to P-rich assembly machinery and therefore a lower N:P ratio. P-limited environments favour slightly less allocation to assembly than N-limited or light-limited environments. The model predicts that optimal N:P ratios will vary from 8.2 to 45.0, depending on the ecological conditions. Our results show that the canonical Redfield N:P ratio of 16 is not a universal biochemical optimum, but instead represents an average of species-specific N:P ratios.     

The evolutionary inheritance of elemental stoichiometry in marine phytoplankton

Phytoplankton is a nineteenth century ecological construct for a biologically diverse group of pelagic photoautotrophs that share common metabolic functions but not evolutionary histories. In contrast to terrestrial plants, a major schism occurred in the evolution of the eukaryotic phytoplankton that gave rise to two major plastid superfamilies. The green superfamily appropriated chlorophyll b, whereas the red superfamily uses chlorophyll c as an accessory photosynthetic pigment. Fossil evidence suggests that the green superfamily dominated Palaeozoic oceans. However, after the end-Permian extinction, members of the red superfamily rose to ecological prominence. The processes responsible for this shift are obscure. Here we present an analysis of major nutrients and trace elements in 15 species of marine phytoplankton from the two superfamilies. Our results indicate that there are systematic phylogenetic differences in the two plastid types where macronutrient (carbon:nitrogen:phosphorus) stoichiometries primarily reflect ancestral pre-symbiotic host cell phenotypes, but trace element composition reflects differences in the acquired plastids. The compositional differences between the two plastid superfamilies suggest that changes in ocean redox state strongly influenced the evolution and selection of eukaryotic phytoplankton since the Proterozoic era.     

浮游植物光合色素的提取方法

光合色素是评价浮游植物生物量和生产力的重要指标,是海洋调查中必不可少的生化参数,而进行色素分析的首要步骤就是将色素从浮游植物中提取出来。色素提取的效率决定于溶剂的渗透力和溶解能力,而不能单单依赖机械破碎。文章综述了浮游植物光合色素的三种主要提取技术:直接浸泡提取法、浸泡研磨提取法和超声波破碎浸泡法,并从提取能力、保真性、广泛适用性、准确性、简单和安全六个方面进行评价。得到将DMF萃取液再超声破碎是最佳的提取方法,所有色素的提取率几乎达到100%。     

废水除磷技术的发展趋势

研究表明,多数富营养化水体中的控制因素为磷,文章介绍了近些年来废水除磷的方法、机理及优缺点,并进一步介绍了废水除磷的现状、发展与动向.     

瓯江大溪的浮游藻类与水体污染

根据 1 999年 5月至 2 0 0 0年 4月对瓯江大溪的统计调查 ,发现有浮游藻类 85种 .藻类的总数和类型与水体污染有关 .在重污染水体中 ,数量最多的是裸藻门、硅藻门和蓝藻门 .     

百花湖表层沉积物磷的化学形态及pH值对磷释放的影响

对百花湖沉积物的总磷、磷形态进行了分析,模拟研究了不同pH值对水体中总溶解性磷和溶解性活性磷含量的影响。结果表明,百花湖沉积物样品总磷含量在503～2351mg／kg,属于中富营养化到富营养化水平。沉积物的磷主要由无机磷组成,其中主要是钙磷。pH值是影响磷释放的重要因素,强酸性及碱性条件下皆利于磷的释放,中性条件磷的释...     

甘南亚高寒草甸金露梅叶片氮磷化学计量学动态

通过甘南地区金露梅的研究,以营养元素的不同水平供给为外部驱动因素,有无繁殖过程为内部因素,比较分析了金露梅叶片氮磷化学计量学的变化特征.研究结果表明:施肥显著影响了叶片的w(N)和w(P),施肥后叶片的w(N)依次为17.8,18.9,20.1,22.6 mg/g,w(P)依次为1.92,2.05,2.19,2.58 mg/g,但施肥对w(N):w(P)的影响不显著.繁殖显著降低了叶片的w(N)和w(N):w(P),而对w(P)影响不显著.外部和内部因素对金露梅叶片的化学计量学的影响不相同.不同的施肥水平显著影响金露梅叶片的w(N)和w(P),而对w(N):w(P)影响不显著.证明繁殖过程导致了氮的大量消耗和w(N):w(P)的显著降低.金露梅在内外因素的影响下分别表现了w(N):w(P)的趋同和分异.     

生物除磷的碳源影响

文章从理论上系统地分析了不同生物除磷工艺的碳源要求 ,以及影响其除磷效果的关键因素。并理论结合实践 ,分析碳源分配对生物脱氮除磷的工艺选择和运行的重要性 ,建议从碳源的角度进行污水除磷设施的优化设计 ,以此开发新的工艺来解决进水碳源成为限制因素的污水处理问题     

河流内源磷释放环境影响因子研究进展

平原地区河流的富营养化已日益受到重视,当外源营养物质的输入得到控制时,河流内源污染物的释放规律研究是防治、修复和治理河流富营养化的重要决策工具.笔者分析了内源磷的赋存形态,总结了影响内源磷释放的环境因子,如pH、温度、溶解氧、微生物的活动、氧化还原电位、周期性的水淹、水生植物、硝酸盐以及河流水动力条件等,指出了当前研究的不足,并提出了相应的解决方法.针对浅水河滨带有水生植物分布的特点,认为不同水动力条件和水生植物对内源磷释放及吸收的影响更具有意义.     

计算机测试形式对语言测试的影响

总结了计算机语言测试的发展现状及其优势,从测试的信度、与传统纸笔测试的对等性和实用性三个主要方面分析计算机测试所面临的挑战,并对计算机语言测试的发展前景做了初步的展望。     

The impact of microRNAs on protein output

MicroRNAs are endogenous approximately 23-nucleotide RNAs that can pair to sites in the messenger RNAs of protein-coding genes to downregulate the expression from these messages. MicroRNAs are known to influence the evolution and stability of many mRNAs, but their global impact on protein output had not been examined. Here we use quantitative mass spectrometry to measure the response of thousands of proteins after introducing microRNAs into cultured cells and after deleting mir-223 in mouse neutrophils. The identities of the responsive proteins indicate that targeting is primarily through seed-matched sites located within favourable predicted contexts in 3' untranslated regions. Hundreds of genes were directly repressed, albeit each to a modest degree, by individual microRNAs. Although some targets were repressed without detectable changes in mRNA levels, those translationally repressed by more than a third also displayed detectable mRNA destabilization, and, for the more highly repressed targets, mRNA destabilization usually comprised the major component of repression. The impact of microRNAs on the proteome indicated that for most interactions microRNAs act as rheostats to make fine-scale adjustments to protein output.     

化学磷回收促进生物除磷效果的试验研究

污水中碳源不足严重影响生物脱氮除磷效果,利用化学除磷宏量效果显著,生物除磷微量作用明显的特点,本试验对少量上清液进行磷沉淀可以相对提高m(C)/m(P)、m(C)/m(N),以达到磷回收和改善处理水质的目的;试验结果表明,在m(COD)/m(P)≤25时,抽取10%进水量的厌氧上清液并调节pH=9,利用进水中业已存在的钙、镁等离子沉淀磷,在m(COD)/m(P)≥20时,出水磷体积质量可恢复至0.5~1 m g/L;通过计算表明,化学除磷后约增加了30%的碳源,同时又可回收20%的磷。     

The decline and fate of an iron-induced subarctic phytoplankton bloom

Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.     

磷浓度对厌氧生物除磷效果及其微生物群落结构

通过厌氧培养基试验,考察了不同起始磷浓度对厌氧生物除磷的影响,并用16S rDNA分子生物学技术PCR-DGGE方法对稳定时期的各种泥样品中微生物群落结构进行跟踪研究.试验结果表明:随着磷浓度的升高,总磷的去除量增加,当总磷含量高于50 mg·L-1时,总磷去除量不随初始磷浓度的升高而升高.稳定培养状态下微生物多样性丰富,不同起始磷浓度污泥样品相似性不高,其中初始磷浓度为20 mg·L-1和60 mg·L-1的厌氧污泥样品相似性最低为67.4％,磷浓度条件可改善微生物群落结构.     

The impact of ocean warming on marine organisms

Since the beginning of the Industrial Revolution during the late eighteenth to the early nineteenth centuries, there has been rapidly increasing release of greenhouse gases, notably CO₂, into the atmosphere. As a consequence of this atmospheric change, the Earth’s average surface temperature has increased by approximately 0.6 °C over the last 100 years. The rate of release of greenhouse gases continues to increase, and global surface temperature rose by approximately 0.2 °C per decade in the last 30 years, a rate that is greater than at any other time during the last 1,000 years. The wide-ranging effects of these increases in greenhouse gases and temperature on the biosphere are subject to intense scientific study. Much has been learned, but much more needs to be elucidated, if we are to predict how terrestrial and aquatic ecosystems will be affected by global change. This brief review focuses on the marine environment and offers a concise summary of some of the important advances in our knowledge about the impacts of global change, including physical and chemical changes of the ocean, as well as the impact of ocean warming on marine organisms. Our analysis also points out areas where critical new information is needed if we are to predict the future of marine ecosystems in a warming world with accuracy.     

酸度对Strandberg结构磷钼酸盐形成的影响

在反应物、反应温度等条件相同的情况下,通过调控溶液的pH值,利用水热合成法得到了（C2H10N2）2[Mo5O15（HPO4）2]（1）、（C2H10N2）3[Mo5O15（PO4）2]·6H2O（2）和（C2H10N2）[Na（H2O）5HPO4]2（3）3个化合物,并通过IR光谱、元素分析、热重分析和单晶X-射线衍射分析进行了表征.结果表明,溶液的pH值不同,生成产物不同.在弱酸性条件下生成Strandberg结构.当溶液为碱性时只得到简单化合物.化合物1和2中存在P2Mo5单元与质子化的乙二胺分子的静电作用.分子间通过N-H…O氢键相连形成无限的三维网状结构.化合物3中P2Mo5单元消失,PO4^3-与质子化的乙二胺构成简单的离子型化合物.PO4^3-单元之间通过O—Na—O桥键和分子间氢键作用形成无限三维孔道结构.     

The case against climate regulation via oceanic phytoplankton sulphur emissions

More than twenty years ago, a biological regulation of climate was proposed whereby emissions of dimethyl sulphide from oceanic phytoplankton resulted in the formation of aerosol particles that acted as cloud condensation nuclei in the marine boundary layer. In this hypothesis--referred to as CLAW--the increase in cloud condensation nuclei led to an increase in cloud albedo with the resulting changes in temperature and radiation initiating a climate feedback altering dimethyl sulphide emissions from phytoplankton. Over the past two decades, observations in the marine boundary layer, laboratory studies and modelling efforts have been conducted seeking evidence for the CLAW hypothesis. The results indicate that a dimethyl sulphide biological control over cloud condensation nuclei probably does not exist and that sources of these nuclei to the marine boundary layer and the response of clouds to changes in aerosol are much more complex than was recognized twenty years ago. These results indicate that it is time to retire the CLAW hypothesis.     

铁接触法除磷机理

分别从金属腐蚀机理和铁盐除磷机理两方面阐述了铁接触法除磷的作用机理,并介绍了铁接触法除磷速率的主要影响因素,进而归纳出铁接触法除磷的定义,为进一步研究铁接触法除磷技术奠定了理论基础。