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1.
The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. We used the fossil record of seep mollusks to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to those of deep-sea taxa, suggesting that seep faunas may be shaped by the factors that drive the evolution of life in the deep sea in general. Our data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events. 相似文献
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以渗水地膜为试材、普通聚乙烯塑料薄膜为对照,对比研究了渗水地膜覆盖对花生叶绿素含量和细胞膜透性的影响.结果表明,渗水地膜覆盖可增加花生叶绿素含量,增强光合作用,减小细胞膜相对透性,从而增加干物质积累,提高花生荚果产量;渗水地膜覆盖可比普通地膜覆盖和露地栽培分别增产9.8%和65.4%. 相似文献
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孙进 《南京农业大学学报》2001,24(1):65-68
根据双层地基的特点，分别对复合土工膜堆石堤堤基采用高压喷射灌浆板墙方案和压重防止管涌流土方案的防渗效果及经济性进行了计算比较，结果表明，高压喷射灌浆板墙方案防渗效果好且经济合理，特别是在广大的山丘区，耕地面积十分紧缺，压重永久占地的情况下，应优先考虑高喷方案。 相似文献
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苹果树盘内埋罐节水渗灌的效应 总被引：6，自引：0，他引：6
以无灌溉条件生长在丘陵地上的8年生红富士苹果树为试材,探讨了树盘内埋罐节水渗灌的生理生产效应,结果表明：树盘埋罐渗灌明显增加了新梢长度、短枝叶叶面积、叶绿素含量、光合和蒸腾速率,提高了树体的水分利用效率和果实的单果重、糖／酸比,降低了果实的可溶性固形物和含酸量。如果埋罐结合施肥。所测定的各项形态和生理指标均显著高于单独埋罐处理,果实品质也得到了改善。另外,各种处理还不同程度地提高了叶片和果实某些矿质元素的含量,降低了果实的N／Ca比。 相似文献
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Rau GH 《Science (New York, N.Y.)》1981,213(4505):338-340
The stable carbon isotope ratios in clam mantle tissues taken from both Galápagos and 21 degrees N hydrothermal vent sites were similar to the unusually low ratios of carbon-13 to carbon-12 previously reported for a Galápagos hydrothermal vent mussel. In marked contrast to these bivalves, vestimentiferan worm tissues from a Galápagos vent had isotope ratios that were higher than those of open ocean biota. These observations suggest that more than one nonpelagic and nonphotosynthetic carbon fixation pathway is of nutritional importance to vent animals, and that at least one of these pathways is common to two geographically separated vent sites. 相似文献
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Deep-sea hydrothermal vent communities exhibit an array of reproductive strategies. Although a few vent species undergo planktotrophic, high-dispersal modes of development, most exhibit relatively low dispersal, but probably free-swimming nonplanktotrophic development. This predominance of nonplanktotrophy may be largely a reflection of phylogenetic constraints on the vent colonizing taxa; intervent dispersal among these forms may be facilitated by reduced developmental rates in the cold abyssal waters away from the vents. It is proposed that for those vent species with nonplanktotrophic development, larval dispersal is a stepwise process with oceanic ridge axes serving as discrete dispersal corridors. 相似文献
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低压微孔地埋管灌溉技术要素试验研究 总被引：4，自引：0，他引：4
结合地上滴灌与渗灌技术优势,提出并进行了地下低压微孔管灌技术要素试验研究,结果认为,条件许可的地方工作压力选择１．５７～２．３５ ｋＰａ 变水头,管径２０ ｍ ｍ ,孔距６０ ｃｍ ,孔径０．７ ｍ ｍ 为最佳管道技术要素;微孔管内的悬浮物质及固体物质易于清洗;管道各孔口出流均匀,土壤湿润理想;并可方便施肥 相似文献
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侧通风口高度对塑料温室气流及温湿度的影响 总被引：1，自引：1，他引：0
为确定降温、除湿等不同环境需求下温室最适侧通风口高度,以陕西省杨凌地区的塑料温室为对象,采用试验和计算流体力学模拟方法,对4种侧通风口高度(40、60、80和100cm)下室内的流场、气温、相对湿度变化及分布均匀性进行研究;模型经过实测验证,模拟值与实测值变化趋势基本吻合,各测点气温和相对湿度的平均相对误差分别为1.2%和2.0%。数值模拟结果表明:不同侧通风口高度的室内平均风速由高到低依次为距地面60、40、80和100cm;温湿度瞬时变化速率随通风口高度升高呈先升高再降低的趋势;侧通风口距地面100cm时,室内的温湿度均匀性最优,60cm的次之,27个测点的温湿度变异系数较同时刻100cm高度仅高出1.1%和3.0%;综合考虑降温及除湿需求,侧通风口距地面60cm时室内气流运动活跃,适合夏季降温排湿和换气补气;在距地面60cm基础上提高侧通风口高度,可在保证除湿效果的同时减缓降温速度,适合冬季保温排湿;降低侧通风口距地高度可减缓室内环境变化速率,适合极端天气下的通风换气需求。 相似文献
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Van Dover CL Humphris SE Fornari D Cavanaugh CM Collier R Goffredi SK Hashimoto J Lilley MD Reysenbach AL Shank TM Von Damm KL Banta A Gallant RM Gotz D Green D Hall J Harmer TL Hurtado LA Johnson P McKiness ZP Meredith C Olson E Pan IL Turnipseed M Won Y Young CR Vrijenhoek RC 《Science (New York, N.Y.)》2001,294(5543):818-823
Within the endemic invertebrate faunas of hydrothermal vents, five biogeographic provinces are recognized. Invertebrates at two Indian Ocean vent fields (Kairei and Edmond) belong to a sixth province, despite ecological settings and invertebrate-bacterial symbioses similar to those of both western Pacific and Atlantic vents. Most organisms found at these Indian Ocean vent fields have evolutionary affinities with western Pacific vent faunas, but a shrimp that ecologically dominates Indian Ocean vents closely resembles its Mid-Atlantic counterpart. These findings contribute to a global assessment of the biogeography of chemosynthetic faunas and indicate that the Indian Ocean vent community follows asymmetric assembly rules biased toward Pacific evolutionary alliances. 相似文献
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Grassle JF 《Science (New York, N.Y.)》1985,229(4715):713-717
Hydrothermal vent communities characterized by large clams, mussels, and vestimentiferan worms thrive on chemosynthetic microbial production. There are similarities in the animal distributions at vent communities from 20 degrees S to 46 degrees N on the Mid-Ocean Ridge in the Pacific Ocean and at cold sulfide seeps in the Gulf of Mexico. Vent communities, consisting of at least 16 previously unknown families of invertebrates, are at least 200 million years old. Since the life-span of a vent is only tens of years, the species survive by rapid growth and widespread dispersal of larvae with the subsequent colonization of new vents. 相似文献
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The probable range of seepage into the marine environment is 0.2 x 10(6) to 6.0 x 10(6) metric tons per year. Within this range the best estimate for the present marine seepage worldwide is on the order of 0.6 x 10(6) metric tons per year. This estimate is based on the presumption that only a few other areas around the world are as seepage-prone as southern California. Measurements of seeps and seepage rates are too few to allow an accurate estimation by observation and measurement techniques alone. Seepage potential can, however, be related to geologic criteria, and these provide sound bases for marine seepage assessment. On the basis of this estimate, areas of high seepage potential contribute about 45 percent of the worldwide seepage, areas of moderate seepage about 55 percent, and areas of low seepage less than 1 percent. The situation varies somewhat from ocean to ocean. In the Pacific Ocean, areas of high seep potential are by far the major contributors. In the Atlantic, Indian, Arctic, and Southern oceans, areas of moderate seep potential are most significant because areas of high seep potential are relatively rare in these realnis. The circum-Pacific area is the area of greatest seepage; it contributes about 40 percent of the world's total. 相似文献
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Brooks JM Kennicutt MC Fisher CR Macko SA Cole K Childress JJ Bidigare RR Vetter RD 《Science (New York, N.Y.)》1987,238(4830):1138-1142
Mussels, clams, and tube worms collected in the vicinity of hydrocarbon seeps on the Louisiana slope contain mostly "dead" carbon, indicating that dietary carbon is largely derived from seeping oil and gas. Enzyme assays, elemental sulfur analysis, and carbon dioxide fixation studies demonstrate that vestimentiferan tube worms and three clam species contain intracellular, autotrophic sulfur bacterial symbionts. Carbon isotopic ratios of 246 individual animal tissues were used to differentiate heterotrophic (8(13)C = -14 to -20 per mil), sulfur-based (8(13)C = -30 to -42 per mil), and methane-based (8(13)C = <-40 per mil) energy sources. Mussels with symbiotic methanotrophic bacteria reflect the carbon isotopic composition of the methane source. Isotopically light nitrogen and sulfur confirm the chemoautotrophic nature of the seep animals. Sulfur-based chemosynthetic animals contain isotopically light sulfur, whereas methane-based symbiotic mussels more closely reflect the heavier oceanic sulfate pool. The nitrogen requirement of some seep animals may be supported by nitrogen-fixing bacteria. Some grazing neogastropods have isotopic values characteristic of chemosynthetic animals, suggesting the transfer of carbon into the background deep-sea fauna. 相似文献
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本文从发生情况、临床表现和尸检变化等多方面对四川省某珍禽养殖场种山鸡啄肛症进行了系统观察，并分析和探讨了发病的原因、特点及防制措施． 相似文献
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为了解东海近海蟹笼逃逸口类型对三疣梭子蟹（Portunus trituberculatus）逃逸行为的影响，本研究使用红外水下摄像装备，对入笼的三疣梭子蟹在不同行为阶段对安装于侧网靠近笼底一侧的刚性矩形逃逸口（40mm高×200mm宽）和网目逃逸口（由2个位置较低的40mm×60mm和1个位置较高的60mm×60mm破目构成）的行为反应进行了观察。根据三疣梭子蟹探索、发现并接近、穿越企图和穿越逃逸口个体连续行为的4个阶段观察结果显示：相比刚性矩形逃逸口，三疣梭子蟹在网目逃逸口实验蟹笼中的探索行为持续时间更长；在笼底探索的个体能定位、发现并接近2种不同类型逃逸口，但发现并接近网目逃逸口时距离入笼的平均时间（P<0.01）和平均次数（P=0.061）均大于刚性矩形逃逸口；约85%发现并接近逃逸口的三疣梭子蟹企图穿越逃逸口，且在逃逸口类型之间没有显著差异；三疣梭子蟹在网目逃逸口前停留了更长的时间（P=0.006），且这一时间显著影响着个体是否企图逃逸的行为。所有个体均采用侧身姿态穿越逃逸口，对于刚性矩形逃逸口，个体甲高与逃逸口高度的关系是决定个体能否成功逃逸的关键因素；对于网目逃逸口，个体优先尝试穿越较低逃逸口，并最终全部逃逸。实验结果表明网目逃逸口可以作为蟹笼渔具逃逸装置，生物可降解材料应用可成为缓解蟹笼幽灵捕捞问题的技术手段之一。 相似文献
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Unusual concentrations of dissolved two- to four-carbon alkanes were observed in the waters in Norton Sound in a localized area approximately 40 kilometers south of Nome, Alaska, in 1976. The hydrocarbons were identified in the near-bottom waters downcurrent for more than 100 kilometers from a sea-floor point source. Preliminary dynamic modeling estimates of the initial gas phase composition predict methanelethane and ethanelpropane ratios of 24 and 1.7, respectively, assuming the hydrocarbons were introduced by bubbles. The low ethanelpropane ratio is indicative of gas from a liquid petroleum source rather than from nonassociated or biogenic natural gas. Preliminary data on the structural geology of Norton Basin lend support to the interpretation based on the hydrocarbon plume. Unconformably truncated strata dip basinward from the seep locus; acoustic anomalies and numerous steeply dipping faults in the immediate vicinity of the seep are corroborating evidence that shallow gas- or petroleum-charged sediments and strata coincide with avenues for migration of mobile hydrocarbons to the sea floor. These factors, taken in concert with the sedimentological regime, the recent revision (increase) of basin depth estimates, and the highly localized hydrocarbon source, strongly suggest a thermogenic rather than a recent biogenic origin for these gaseous compounds. 相似文献
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Kieffer SW 《Science (New York, N.Y.)》1995,269(5229):1385-1391
Volcanic eruptions of gassy magmas on Earth, Venus, and Mars produce plumes with markedly different fluid dynamics regimes. In large part the differences are caused by the differing atmospheric pressures and ratios of volcanic vent pressure to atmospheric pressure. For each of these planets, numerical simulations of an eruption of magma containing 4 weight percent gas were run on a workstation. On Venus the simulated eruption of a pressure-balanced plume formed a dense fountain over the vent and continuous pyroclastic flows. On Earth and Mars, simulated pressure-balanced plumes produced ash columns, ash falls, and possible small pyroclastic flows. An overpressured plume, illustrated for Mars, exhibited a complex supersonic velocity structure and internal shocks. 相似文献