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11.
水淹状况是湿地植被动态的重要影响因素。该研究基于谷歌地球引擎(GEE)平台, 利用2000-03-01至2020-02-29所有覆盖研究区域的MODIS遥感影像数据, 分析20年间水淹频率(IF)、增强型植被指数(EVI)的时空变化以及湿地植被对IF变化的响应, 得出以下结论: (1) 20年来鄱阳湖水文节律发生了明显改变, 高IF (IF > 75%)水域面积呈现下降趋势, 从2000年1 435.3 km2下降至2019年的510.25 km2, 降幅为64.45%; (2)区域平均EVI呈显著上升趋势, 植被扩张主要集中在中部IF下降区域; (3)分析不同总水淹频率区域中平均EVI年际变化, 发现EVI与水淹状况的变化趋势相似, 2009年之后鄱阳湖水域面积萎缩趋势缓解, EVI增长速度出现下降; (4)鄱阳湖湿地植被主要沿水域面积萎缩方向扩张, 基于像元统计20年间IF与EVI的变化趋势, 发现它们在空间分布上高度吻合, 这种空间异质性进一步证实水淹状况起到调节植被动态变化的作用。 相似文献
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The molecular analysis of the genetic systems controlling the main stages of nodule bacteria (rhizobia) interaction with a legume host (signaling at early stages and symbiotic nitrogen fixation) has shown that the widespread recombination of genetic material in free-living ancestors of rhizobia was an important factor in the evolution of these systems. These recombinations could be conditioned by a high content of repeated DNA sequences and the IS elements in the rhizobial genome. A high recombination activity of rhizobia is manifested in the panmictic structure of their populations, which is associated with frequency-dependent selection favoring rare recombinants. This selection is realized through the competition of virulent strains for the nodule formation and can be controlled by the genes whose expression depends on population density (via the quorum sensing mechanism). A high degree of panmixia in rhizobial populations is associated with their ecotypic polymorphism, manifested as the coexistence of symbiotic and nonsymbiotic strains. This type of polymorphism is caused by individual selection during the periodic changes of ecological niches (soil-plant host) in the rhizobia life cycle. The rhizobia-plant interaction stimulates selection in bacterial populations, which results in the increased levels of their heterogeneity and panmixia. The combination of individual and frequency-dependent selection types resulted in the high rates of symbiosis evolution and polyphyletic origin of diverse rhizobial species. 相似文献
13.
Soil inorganic carbon storage pattern in China 总被引:1,自引:0,他引:1
NA MI SHAOQIANG WANG JIYUAN LIU GUIRUI YU WENJUAN ZHANG ESTEBAN JOBBÁGY 《Global Change Biology》2008,14(10):2380-2387
Soils with pedogenic carbonate cover about 30% (3.44 × 106 km2) of China, mainly across its arid and semiarid regions in the Northwest. Based on the second national soil survey (1979–1992), total soil inorganic carbon (SIC) storage in China was estimated to be 53.3±6.3 PgC (1 Pg=1015 g) to the depth investigated to 2 m. Soil inorganic carbon storages were 4.6, 10.6, 11.1, and 20.8 Pg for the depth ranges of 0–0.1, 0.1–0.3, 0.3–0.5, and 0.5–1 m, respectively. Stocks for 0.1, 0.3, 0.5, and 1 m of depth accounted for 8.7%, 28.7%, 49.6%, and 88.9% of total SIC, respectively. In contrast with soil organic carbon (SOC) storage, which is highest under 500–800 mm yr−1 of mean precipitation, SIC storage peaks where mean precipitation is <400 mm yr−1. The amount and vertical distribution of SIC was related to climate and land cover type. Content of SIC in each incremental horizon was positively related with mean annual temperature and negatively related with mean annual precipitation, with the magnitude of SIC content across land cover types showing the following order: desert, grassland >shrubland, cropland >marsh, forest, meadow. Densities of SIC increased generally with depth in all ecosystem types with the exception of deserts and marshes where it peaked in intermediate layers (0.1–0.3 m for first and 0.3–0.5 m for latter). Being an abundant component of soil carbon stocks in China, SIC dynamics and the process involved in its accumulation or loss from soils require a better understanding. 相似文献
14.
利用水蒸气蒸馏法提取小黄皮叶挥发油,运用毛细管气相色谱-质谱联用法对挥发油进行了分析,分离出40个峰,鉴定了其中的37种成分,所鉴定成分占挥发油总量的99.87%,其主要化学成分为单萜及倍半萜类化合物。 相似文献
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肠道病毒71型作为引起儿童群体常见传染性手足口病(HFMD)的主要病原,具有导致少量感染个体出现脑炎等神经系统病变以及相关心肺功能衰竭的病理学特性.因此其预防性疫苗的研发具有重要的公共卫生意义.在前期工作的基础上,一种EV71灭活病毒疫苗(人二倍体细胞)在本研究中基于恒河猴婴猴模型进行了相应的免疫保护性分析.以160EU剂量对2~3月龄婴猴进行0,4周免疫后,动物在第4周接受了剂量为10。~CCID50的病毒经呼吸道的攻击.对病毒攻击后动物在14天内的临床症状、血液生物学、器官病原学分布以及病理学检测的动态观察表明,经疫苗免疫的动物未出现对照动物所具有的特征性临床表现,其血液生物学及病理学检测均无异常.同时,器官病原学分布亦呈阴性.结合动物中和抗体的明确增长及对照动物的综合表现分析,本文的工作证实了该EV71灭活病毒疫苗(人二倍体细胞)在恒河猴婴猴体内的免疫保护性. 相似文献
17.
T. NGAMSIRI Y. OHASHI N. SUKUMASAVIN M. NAKAJIMA U. NA‐NAKORN N. TANIGUCHI 《Molecular ecology resources》2006,6(2):313-315
Microsatellite DNA markers for a critically endangered Mekong giant catfish (Pangasianodon gigas Roberts and Vidthayanon, 1991) were developed from fin clips collected from captive fish using (GT)15 probe. The number of alleles per locus ranged from two to four. The expected heterozygosities ranged from 0.13 to 0.68. Also, these primers were successfully amplified in four closely related species, Pangasius bocourti, Pangasius conchophilus, Pangasius larnaudii and Pangasius sanitwongsei with the number of alleles per locus ranged from 1 to 13, 1 to 16, 1 to 12 and 1 to 4, respectively. These markers should prove to be very useful for the evaluation of genetic diversity for this species and other related Pangasius species. 相似文献
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从茎花葱臭木种子中分离得到5个化合物,经理化与波谱分析鉴定为β-谷甾醇(1)、没食子酸乙酯(2)、胡萝卜苷(3)、1-O-β-D-吡喃葡萄糖基-(2S,3S,4R,8Z)-2-N-(2 ′-羟基二十四烷酰氨基)十八二氧鞘氨-8-烯(4)和2,3,2″,3″-四氢穗花杉双黄酮(5).这5个化合物均首次从该植物中分离得到.其中化合物5进行细胞毒活性测试,没有显示抑制活性. 相似文献
20.
从大苞藤黄枝叶的混合粉碎物中分离到11个化合物,运用光谱手段分别鉴定为neobractatin(1),brasixanthone B (2),5-O-methylxanthone V1 (3),10-O-methylmacluraxanthone (4),isobractatin (5),xanthone V1(6),xerophenone A (7),xerophenone B (8),bractatin (9),macluraxanthone (10)和3-O-methylneobractatin (11).本文首次应用超高效液相色谱-质谱联用技术分离了异构体7和8并测定了其精确分子量.其中化合物6~8为首次从该植物中发现. 相似文献