974 resultados para reed marsh


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本研究利用酵母功能互补方法和RACE的方法从具有较强抗逆能力的绊根草中克隆了9个与重金属抗性相关的克隆,并对部分基因的表达调控及功能进行了初步研究。同时还利用细胞工程技术筛选到了具有较强的耐受火箭推进齐-偏二甲肼(UDMH)的芦苇的变异株系,为以后用人工湿地系统处理受偏二甲肼污染的废水奠定了基础。 本研究通过酵母功能互补法克隆到了五个基因,分别为CdSRP、CdTETH、 CdASP、CdMT2和CdTER1。CdSRP可能是一种衰老相关基因;CdTETH编码的产物可能是组成TRAPP复合体的一个亚基;CdASP是一个功能未知的基因;CdMT2是一个编码Type Ⅱ型金属硫蛋白基因;CdTER1可能是编码一个TERl-like家族蛋白成员的基因。用这五个基因分别转化因Acr基因缺失而对As敏感的酵母菌株FD236-6A,所获得的转化子对As的抗性均有提高,其中以CdMT2、CdTER1和CdASP的作用最为明显。这些基因的表达调控方式以及与其它重金属抗性的关系正在研究中。 本研究还利用RACE的方法克隆了一个谷胱甘肽S-转移酶基因,CdGSTFl;两个植物络合素合酶基因,CdPCSI和CdPCSⅡ,和一个TypeⅠ型金属硫蛋白基因CdMT1。CdGSTF1属于phi类GST基因,Northern-blotting分析表明,CdGSTF1在绊根草根部的表达受Cd2+的诱导,暗示其可能具有解除氧自由基或氢过氧化物的毒性的作用。CdPCSI和CdPCSⅡ的同源性较高,表明绊根草含有两个以上的PCs合酶的基因。参照前人的方法对CdPCSI和CdPCSII的氨基酸序列进行分析,发现它们含有六个非常相近的Cd2+结合位点,这两个基因的功能及其调控方式有何差异尚需进一步的研究。cdMT1与用酵母功能互补法克隆到的CdMT2属于不同类型的MT基因,对它们之间很可能存在的功能、组织特异性等方面的差异性进行了讨论。 四氧化二氮/偏二甲肼是常用的航天器双组元液体推进剂。偏二甲肼易挥发,有致癌、致畸、致突变的毒性。在推进剂贮存、运输、转注、火箭发动机试车、火箭发射、管道及设备冲洗中产生的含有偏二甲肼的废水能够对卫星发射基地的地下水源和空气造成污染。因此迫切需要培育能够净化偏二甲肼污水的植物。 本研究利用生长在卫星发射基地的野生芦苇的种子诱导愈伤组织,进而通过逐步提高偏二甲肼筛选压力的方式从中筛选出具有较强抗性的愈伤组织,然后诱导其分化。目前已经得到能够在含有1.63 mmol/L和3.26 mmol/L偏二甲肼的分化培养基中生长良好的芦苇再生苗,并已成功转移至温室中。抗性分化苗对污水的处理效果和耐受偏二甲肼的机理正在研究中。

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植物在长期的进化过程中,已经对其生存环境具备了各种适应对策。放牧影响下草原植物的生态适应策略,决定了其是否能够忍耐或者适应放牧生境从而维持自身的生存和种群的延续。研究植食性动物对植物的影响有助于制定合理的放牧制度和草地利用方式,从而为防止草原退化和恢复退化草地提供重要的理论依据;同时研究植物对放牧的响应策略,对于草原生物多样性的保护和草原生物资源的合理利用具有重要的理论和实践意义。 本文以中科院内蒙古草原生态系统定位研究站放牧综合试验样地中的小叶锦鸡儿为主要研究对象。通过长期不同放牧强度的放牧试验和唾液涂抹等模拟试验,从形态学、有性生殖、种子萌发和遗传多样性等方面,探讨了小叶锦鸡儿对放牧家畜(绵羊)采食的生物学响应。本研究得到以下主要结论: 1. 通过小叶锦鸡儿形态和有性生殖的实验,可以看到放牧改变了该种植物的形态和生殖特性,不同放牧强度对其影响的程度是不相同的。在啃食压力下,小叶锦鸡儿的营养、生殖和防御之间存在消长关系。随着放牧强度的增加,小叶锦鸡儿对营养器官和有性生殖器官的投资均减少,而对防御器官的投资有增加的趋势,主要体现在:个体的小型化(植株高度、叶轴长度、小叶大小)和果荚数目及成熟种子数都随着放牧强度的增加而明显减少;物理性防御器官――刺,其密度和长度都明显的增加。同时,放牧也对植物花粉的品质产生了消极影响。 2. 放牧不仅影响了植物体本身的生物学特性,而且影响了子代的生物学特性。不同放牧强度下的植株产生的种子,其萌发速率明显不同。同时放牧强度和沙埋深度对小叶锦鸡儿的出苗率均具有显著影响,随着沙埋深度增加,出苗率明显降低,0~2cm是其适宜出苗的沙埋深度;浅层沙埋处理下,轻度放牧和重度放牧的出苗率差异显著。与轻度放牧相比,重牧条件下同一沙埋深度的种子出苗时间明显推迟;在相同放牧压力下,沙埋深度也影响了出苗时间。 3. 采食活动对植物本身的形态、生殖以及子代的萌发特性都产生了影响;通过AFLP实验证明了小叶锦鸡儿在长期的放牧历史活动中已经发生了遗传多样性的变化,重度放牧强度下的植株与轻度放牧条件下的植株具有相对较远的遗传距离,也就是说,小叶锦鸡儿种群的分化与放牧强度具有密切的关系。 4. 三种不同生活型植物(灌木-小叶锦鸡儿、半灌木-冷蒿和草本-羊草)对绵羊唾液涂抹的响应不同,刈割和涂抹绵羊唾液能够增加植物的净地上生物量,并促进植株增加地上部分的光合产物投资。同时表明,简单的机械剪除不能够真正反应放牧家畜采食所产生的生物学效应。

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EXTRACT (SEE PDF FOR FULL ABSTRACT): Pollen analysis and 5 radiocarbon dates for a 687-cm core provide a detailed chronology of environmental change for San Joaquin Marsh at the head of Newport Bay, Orange County, California. Sediment deposition kept pace with sea level rise during the mid-Holocene, but after 4500 years BP, sea water regularly reached the coring site, and salt marsh was the local vegetation. Brief periods of dominance by fresh-water vegetation 3800, 2800, 2300 and after 560 years BP correlate global cooling events and (except the 3800-year BP event) with carbon-14 production anomalies. The coincidence of climate change and carbon-14 anomalies support a causal connection with solar variability, but regardless of the causal mechanism(s) the delta-carbon-14 curves provide a chronology for global, high-frequency climatic change comparable to that of Milankovitch cyclicity for longer time scales.

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辽河三角洲优越的植被生态系统维系着多种生态功能,使该地区成为全国著名的商品粮基地、造纸原料基地和旅游基地。但是,气候变化和人为干扰使得辽河三角洲的植被结构发生了显著变化,影响到植被功能的发挥。 为了应对气候变化和人为干扰对辽河三角洲植被造成的不利影响,本论文围绕植被结构和生产功能,从空间和时间方面,重点阐述了辽河三角洲植被的结构及其驱动机制;辽河三角洲植被生产功能及其驱动机制。 采用的研究方法包括遥感解译、样带调查和全面调查。通过遥感解译方法获取各植被类型的面积、分布及其变化信息,以研究植被的空间分布格局及其变化。通过样带调查方法,获取植被类型、土壤和水文等信息,并结合规范对应分析和偏相关分析等,研究植被空间分布格局的驱动机制。通过全面调查方法,获取植被净第一性生产力、粮食产量、土壤和水文等信息,并结合地理信息系统(GIS)的插值分析和相关分析等,研究植被生产功能的空间分布格局及其驱动机制。主要结论如下: 1. 植被组成和空间格局:辽河三角洲植被主要由自然湿地植被、人工湿地植被、自然旱地植被、人工旱地植被四大植被类型组成。其中,面积最大的3种植被是玉米、水稻和芦苇。四大植被类型以双台子河口为中心,基本上呈现半环状分布格局。 2. 植被空间格局变化:1988~2006年辽河三角洲植被空间格局发生了显著变化,主要植被类型分布趋于集中,形成了一些较大的斑块,而不是离散和破碎。从面积上看,水稻是面积增加最多的植被类型;玉米是面积减少最多的植被类型。从变化速率看,水稻、玉米和芦苇的变化幅度都较大,分别为33.2%、-16.1%和-23.2% 。 3. 植被空间格局形成机制:辽河三角洲植被分布格局不是由气候因子决定的,而是由土壤因子决定。土壤可溶性盐是决定植被分布格局最重要的环境因子,其次是土壤含水量。 4. 植被生产功能:辽河三角洲植被具有极高的生产力。其中,玉米、水稻和芦苇3种主要植被的地上净第一性生产力分别为30,485、18,248和17,440 kg/(ha•a)。玉米和水稻单位面积粮食产量也非常高,分别为14,813和10,365 kg/(ha•a)。 5. 植被生产功能年际变化:辽河三角洲植被生产力存在明显的年际波动。1992~2005 年间玉米和水稻粮食产量呈现显著的年际波动;1949~1990 年间芦苇产量不仅存在较明显的年际波动,而且呈现非常显著的增加趋势。 6. 植被生产功能年际变化的驱动机制:气候因子是玉米和水稻粮食产量年际变化的主要驱动因子,气候因子对玉米和水稻粮食产量的影响远远大于人为因子(农业人口、施肥量、灌溉面积)的影响。气候因子和人为因子对芦苇产量年际变化的影响都非常显著。在气候因子中,年日照数是驱动玉米产量年际波动的主导气候因子;年降水量是驱动水稻产量年际波动的主导气候因子;年蒸发量是驱动芦苇产量年际波动的主导气候因子。 7. 植被生产功能空间格局:植被地上净第一性生产力存在显著的空间差异,表现为一种环形空间分布格局,三角洲中部较低,四周地区较高。这种空间分布格局表明,在辽河三角洲,植被地上净第一性生产力最高的不是湿地植被,而是周围旱地植被。 8. 植被生产功能空间格局的形成机制:土壤含水量和海拔是驱动辽河三角洲植被生产力空间格局的主要因子;土壤盐度、土壤pH和土壤容重对植被生产力的空间格局影响不大。土壤营养元素(氮、磷、钾) 对植被生产力的空间格局几乎没有影响。

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This report reviews some of the natural ecological processes at work within a salt marsh as they relate to a spill of natural gas condensate - a mixture of aliphatic hydrocarbons, n-hexane, benzene, toluene, and xylene. It also reviews the environmental impacts of some of the components of natural gas condensate as well as related compounds (crude oil, higher molecular weight hydrocarbons, polycyclic aromatic hydrocarons - PAHs, linear alkyl-benzenes - LABs, etc.) on salt marsh ecosystems in southern Louisiana and elsewhere in the world. The behavior and persistence of these compounds once they have entered the environment is also considered.

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A novel optical switching matrix measuring 1×2 mm2 in size is fabricated. The switching matrix is composed of waveguides, four 1×4 multimode interference (MMI) splitters, 32 total internal refraction mirrors and four 4×1 MMI combiners with the extremely compact size of 1×2 mm2. This integrated device are assessed and loss contribution measured from test structure is presented.

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Quantum well intermixing is a key technique for photonic integration. The intermixing of InP/InGaAs/InGaAsP material involving the deposition of a layer of sputtered SiO2 on the semiconductor surface, followed by thermal annealing has allowed good control of the intermixing process and has been used to fabricate extended cavity lasers. This will be used for optimization of the performance of optical switches consisting of passive components, modulators and amplifiers.

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We have fabricated an ultra-compact 4×4 optical matrix on InP/InGaAsP material. 1×4 MMI couplers and TIR mirrors are employed to produce a compact 1×2 mm2 device. A CH4/H2/O2 RIE dry etch process has been used to realize two-level dry etching: deep-etch for both the MMI couplers and the mirrors and shallow-etch for the rest of the routing waveguides. It was found that a metal/dielectric bilayer mask is essential for multi-dry-etch processes and high profile verticality. We have found a Ti intermediate mask for the deep-etch process which is removable by SF6 dry-etch before the following shallow process. Dry-etch removal of the intermediate mask is necessary to protect the deep-etched mirror sidewall.

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The primary objective in doing this work was to become acquainted with as many forms as possible of the marine fauna of the intertidal zone and if possible to determine some of the environmental relationships which exist in as many different types of habitats as possible. Due to limited amount of time spent in this study no very intensive work could be done and only a general survey was made of the more conspicuous forms of life which were encountered. Most of the work consisted of collecting and observing animals in the tide pools during periods of low tides. The animals collected were then taken to the laboratory and observed and determined as to species. Notes were taken as to place, time, and situation under which the animals were found. As many different types of habitats as possible were visited which included rocky intertidal areas of Mussel Point, Point Pinos, Lighthouse Point, Pescadero Point and Carmel Point just east of Carmel Beach. Sandy beaches were visited at Monterey Beach, Carmel Beach and Asilomar Beach. A marine estuary habitat was visited at Elkhorn Slough. More than two hundred species were identified and observed during this six-week period. A rather hasty population study was made of the eelgrass, Phyllospadix, of the intertidal zone at Mussel Point and of an algae, Gigartina caniculata, which grows at the level just above the eelgrass.

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The study was conducted to determine the effects of varying concentrations of ammonia to milkfish fry. Two runs of static 96h bioassays were conducted to determine the median lethal concentration (LC 50) of unionized ammonia (NH3) to milkfish fry. Test concentrations were based on exploratory 24h and 48h bioassays and were made in three replicates. Reagent grade ammonium chloride (NH4Cl) was used to adjust the level of unionized ammonia. The 96h median lethal concentration, determined by the Reed Muench method was calculated at 28.029 ppm NH3 29.69 ppm. Even at high concentrations of unionized ammonia, most of the fry mortality occurred after 48 to 96 hours exposure. Severe gill damage occurs only at concentrations above 20 ppm, especially above the LC 50. The high LC 50 value obtain shows that milkfish fry has great tolerance to ammonia, that even fry with severely-damaged gills can still recover days after it is returned to favorable culture condition. The result suggest that observed mortalities of milkfish fry under culture conditions are not due to ammonia toxicity.

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One of the most endangered populations of Black-necked Cranes (Grus nigricollis), the central population, is declining due to habitat loss and degradation, but little is known about their space use patterns and habitat preferences. We examined the space use and habitat preferences of Black-necked Cranes during the winter of 2007-2008 at the Napahai wetland in northwest Yunnan, China, where approximately 300 Black-necked Cranes (>90% of the total central population) spent the winter. Euclidean distance analysis was employed to determine the habitat preferences of Black-necked Cranes, and a local nearest-neighbor, convex-hull construction method was used to examine space use. Our results indicate that Black-necked Cranes preferred shallow marsh and wet meadow habitats and avoided farmland and dry grassland. Core-use areas (50% isopleths) and total-use areas (100% isopleths) accounted for only 1.2% and 28.2% of the study area, respectively. We recommend that habitat protection efforts focus on shallow marsh and wet meadow habitats to maintain preferred foraging sites. Core-use areas, such as the primary foraging areas of Black-necked Cranes, should be designated as part of the core zone of the nature reserve. Monthly shifts in the core-use areas of the cranes also indicate that the reserve should be large enough to permit changes in space use. In addition to preserving habitat, government officials should also take measures to decrease human activity in areas used by foraging Black-necked Cranes.

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Despite their ecological and socio-economic importance, Lake Victoria's adjoining "swamps" and lake interface are among the least investigated parts of the lake. The "swamps" a term commonly equated to "wastelands" and the difficult working environment they present in comparison to open water, are major factors for the low level of attention accorded to shoreline wetlands. Moreover, definitions of wetlands highlighted for example in the Ramsar Convention as "areas of marsh, fern, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh or brackish, or salt, including areas of marine water, the depth of which does not exceed six metres" (Ramsar, 1971) were designed to protect birds (water fowl) of international importance. The Ramsar definition, which also includes oceans, has till recently been of limited use for Lake Victoria, because itdoes not fully recognise wetlands in relation to other public concerns such as water quality, biodiversity and the tisheries that are of higher socioeconomic priority than waterfowl. Prior to 1992, fishery research on Lake Victoria included studies of inshore shallow habitats of the lake without specific reference to distance or the type of vegetation at the shore. Results of these studies also conveniently relied heavily on trawl and gill net data from the 5-10 m depth zones as the defining boundary of shallow inshore habitats. In Lake Victoria, such a depth range can be at least one kilometre from the lake interface and by the 10m depth contour, habitats are in the sub-littoral range. Findings from these studies could thus not be used to make direct inferences on the then assumed importance of Lake Victoria wetlands in general.

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Inference for latent feature models is inherently difficult as the inference space grows exponentially with the size of the input data and number of latent features. In this work, we use Kurihara & Welling (2008)'s maximization-expectation framework to perform approximate MAP inference for linear-Gaussian latent feature models with an Indian Buffet Process (IBP) prior. This formulation yields a submodular function of the features that corresponds to a lower bound on the model evidence. By adding a constant to this function, we obtain a nonnegative submodular function that can be maximized via a greedy algorithm that obtains at least a one-third approximation to the optimal solution. Our inference method scales linearly with the size of the input data, and we show the efficacy of our method on the largest datasets currently analyzed using an IBP model.