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391.
微卫星的发展主要受限于微卫星及其旁侧特异引物区的分离,在中国明对虾(Fenner-openaeus chinensis)中建立了选择性扩增多态微卫星位点(SAMPL,selective amplified mic-rosatellite polymorphic loci)技术体系,并初步尝试了基于SAMPL的一种微卫星筛选方法。通过5′端锚定引物引入微卫星序列,对传统SAMPL技术加以改进并以期富集简单重复序列。从测序胶上随机选择5条SAMPL条带(分别命名为S11,S13,S14,S22,S24)克隆测序,大小分别为161,157,147,152,298。其中S11,S13,S14,S22四个片段两端引物分别为AFLP选择性引物和SAMPL引物,S13和S22含微卫星序列重复,S24两端引物均为传统的AFLP引物,在此片断中有一(AG)39重复。 相似文献
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393.
Arthropods living in the canopies of two woody shrub species (a sub-shrub (Gutierrezia sarothrae) and a large shrub (Prosopis glandulosa)) and perennial grasses plus associated herbaceous species, were sampled on 18, 0.5 hectare plots in a Chihuahuan Desert grassland for five consecutive years. Mesquite shrubs were removed from nine plots, six plots were grazed by yearling cattle in August and six plots were grazed in February for the last 3 years of the 5 year study. Arthropod species richness ranged between 154 and 353 on grasses, from 120 to 266 on G. sarothrae, and from 69 to 116 on P. glandulosa. There was a significant relationship between the number of families of insects on grass and G. sarothrae and growing season rainfall but species richness was not a function of growing season rainfall on any of the plants. Several of the arthropod families that were the most species rich in this grassland were found on all of the plants sampled, i.e. Salticid spiders, Bruchid and Curculionid beetles, Cicadellid and Psyllid homopterans, and ants (Formicidae). There were more species rich families that were shared by grasses and the sub-shrub G. sarothrae than with mesquite. The absence of a relationship between growing season rainfall and species richness was attributed to variation in life history characteristics of arthropods and to the non-linear responses of annual and perennial desert grassland plants to rainfall.There were no significant differences in insect family or species richness on any of the plant types as a result of removal of mesquite (P. glandulosa) from selected plots. Intense, short duration (24 h) grazing by livestock during in late summer resulted in reduced species richness in the grass-herb vegetation layer but had no effect on insect species richness on snakeweed or mesquite shrubs. Livestock grazing in winter had no effect on insect species richness on any of the vegetation sampled. 相似文献
394.
The effect of intensive grazing and browsing of domestic stock and wildlife on the number of species and abundance of vegetation was investigated in the Hoanib River catchment, north-western Namibia. The seasonal abundance of ground cover, bare earth, canopy cover, annual grass, perennial grass and annual forbs were measured in each of the focus-study areas. In three of the focus areas where the ranges of both domestic stock and wildlife were restricted either by fencing or water availability, impact on the vegetation was greatest. The final focus area was a more ‘open range’ system that allowed for the free movement of wildlife. Under these conditions the species abundance and availability of browsing and grazing was greater than the other focus areas during both the wet and dry seasons. However, very little difference in abundance and availability of vegetation was observed between focus areas in both seasons regardless of landuse. There is generally a low abundance of perennial grasses and browse species affording the ecosystem little resistance and resilience to disturbance caused by grazing and drought. 相似文献
395.
Primary production in Lake Hayward, Western Australia, is dominated by benthic microbial communities, with limited planktonic
primary production. This study investigated the question of howArtemia, commonly regarded as simple, obligate, non-selective filter feeders, were able to survive in this system. Bacteria (heterotrophic
and autotrophic, filamentous and unicellular) were the major components in the diet of theArtemia in Lake Hayward. These bacteria were derived from bacterial aggregates in the water column and also from benthic mat material
(both still attached to the substrate and from pieces floating in the water column). Benthic diatoms were a substantial dietary
component of animals living in the unstratified shallow regions. Photosynthetic eukaryotic nanoplankton comprised a minor
component of the diet of thisArtemia population. Gut contents of a large number of animals and the results of a simple laboratory test indicated that these animals
utilise substrate-bound food resources. The results of the present study raises the question of the ecological significance
of surface grazing by brine shrimps in other shallow, benthos dominated saline systems. 相似文献
396.
397.
JIANG Xuejun) )* YAO De) LIN Xuehui) ZHAI Shikui)) College of Geoscience Ocean University of China Qingdao P. R. China ) Qingdao Institute of Marine Geology China Geological Survey P. R. China ) College of Georesources Environmental Engineering Sh ong University of Technology Zibo P. R. China 《中国海洋大学学报(英文版)》2009,8(1):57-64
A series of selective dissolution experiments were conducted on the hydrogenic ferromanganese crusts collected near Line Island to study the geochemistry of Mn, Fe, Cu, Co, Ni and Ti. Despite of the fact that the very close intergrowth between amorphous ferric oxyhydroxides and δ-MnO2 exists in the hydrogenic ferromanganese crusts, there is no isomorphous substitution between iron and manganese. This is because the two elements in oxides have different crystal chemistry and geochemistry, such assertion bein... 相似文献
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399.
The effects of vertical sampling resolution on estimates of plankton biomass and grazing calculations were examined using data collected in two different areas with vertically stratified water columns. Data were collected from one site in the upwelling region off Oregon and from four sites in the Northern Gulf of Mexico, three within the Mississippi River plume and one in adjacent oceanic waters. Plankton were found to be concentrated in discrete layers with sharp vertical gradients at all the stations. Phytoplankton distributions were correlated with gradients in temperature and salinity, but microzooplankton and mesozooplankton distributions were not. Layers of zooplankton were sometimes collocated with layers of phytoplankton, but this was not always the case. Simulated calculations demonstrate that when averages are taken over the water column, or coarser scale vertical sampling resolution is used, biomass and mesozooplankton grazing and filtration rates can be greatly underestimated. This has important implications for understanding the ecological significance of discrete layers of plankton and for assessing rates of grazing and production in stratified water columns. 相似文献
400.
在青海海北高寒矮嵩草草甸设置封育禁牧(CK)、轻牧(LG)、中牧(MG)和重牧(HG)放牧梯度试验样地, 进行了土壤速效氮变化特征及影响因素的分析. 结果表明: 植物生长期的5-9月, 土壤NH4+-N、NO3--N和速效氮(NH4+-N和NO3--N之和)含量季节变化明显, 基本表现为植物生长初期高, 末期低. CK、LG、MG和HG条件下, 5-9月0~40 cm土壤NH4+-N平均含量分别为17.62 mg·kg-1、17.84 mg·kg-1、18.63 mg·kg-1和16.67 mg·kg-1, NO3--N平均含量为8.91 mg·kg-1、8.23 mg·kg-1、7.99 mg·kg-1和7.94 mg·kg-1, 速效氮平均含量为26.53 mg·kg-1、26.07 mg·kg-1、26.62 mg·kg-1和24.61 mg·kg-1, 基本表现出随放牧强度增大而降低. 土壤速效氮月际变化与地上绿体生物量具有一定的负相关关系, 表明地上生物量越大, 消耗土壤速效氮越趋明显; 与枯落物有一定的正相关关系, 与地下生物量关系不甚明显, 与湿沉降呈现负的相关性. 土壤NH4+-N含量与土壤有机碳有负相关关系, 而NO3--N含量与有机碳相关性差, 表明土壤有机碳越高, 土壤NH4+-N消耗越明显. 相似文献