Impact of ENSO on East African ecosystems: a multivariate analysis based on climate and remote sensing data

1 The El Niño‐Southern Oscillation (ENSO) is an important driver of inter‐annual variations in climate and ecosystem productivity in tropical regions. Most previous studies have analysed ENSO‐induced changes in climate based on a single variable, such as rainfall. Also, it is generally assumed that the ENSO impact in East Africa is geographically uniform. 2 The objective of this study is to improve understanding of the impact of ENSO on East African ecosystems, by measuring teleconnections between an ENSO index and a number of ecosystem variables in a spatially explicit way and for different time lags. We analysed the spatial patterns of teleconnections in the region by combining time series of climate variables measured for meteorological stations with time series of a vegetation index and surface temperature data measured by remote sensing. 3 Our results confirm the ENSO impact on the climatic and ecological variability in East Africa. However, the pattern of teleconnections is much more complex than generally assumed, both in terms of spatial distribution and impact on different ecosystem variables. Not all climate and land surface variables are teleconnected to ENSO in the same way, which leads to a complex impact of ENSO on the ecosystem. Moreover, the ENSO impact is highly differentiated in space, as the direction, magnitude and timing of this impact are controlled by the local climate system, the presence of large lakes, proximity to the coast and, possibly, local topography and land cover.     

雪后海北高寒草甸地区根田鼠种群特征的变化

根田鼠 (Ｍｉｃｒｏｔｕｓｏｅｃｏｎｏｍｕｓ)是一种分布广泛的小型哺乳动物[1 ] ,在海北高寒草甸地区 ,根田鼠是优势小型啮齿动物之一 ,主要分布于植被较好的草甸和灌丛中 ,有关其自然以及实验状态下种群数量动态的研究相对较多[2～6] ,但是对该地区冬季恶劣自然条件下 ,其种群动态的研究尚未见报道。研究冬季根田鼠种群特征的变化有助于对其整个生活史过程的全面理解 ,也便于了解冬季恶劣气候条件对其越冬留存率的影响进而又是如何影响翌年的种群数量。为此 ,作者于 2 0 0 0年 1 0月和 1 2月在海北高寒草甸生态系统定位站地区对根田鼠种…     

Genetic Diversity of Gli-1，Gli-2 and Glu-1 Alleles Among Chinese Endemic Wheats

Genetic diversity at Gli-1, Gli-2 and Glu-1 loci was investigated in 32 accessions of Chinese endemic wheat by using acid polyacrylamide gel electrophoresis (APAGE) and sodium dodecyl sulfate (SDS)-PAGE. There were 8 gliadin and 3 high-molecular-weight (HMW)-glutenin patterns in 14 Yunnan hulled wheat ( Triticum aestivum ssp. yunnanese King) accessions, 9 gliadin and 4 HMW-glutenin patterns in 9 Tibetan weedrace ( T. aestivum ssp. tibetanum Shao ) accessions, and 9 gliadin and 5 HMW-glutenin patterns in 9 Xinjiang rice wheat ( T. petropavlovskyi Udacz. et Migusch.) accessions. One accession (i.e. Daomai 2) carried new subunits 2.1+10.1 encoded by Glu-D1 . Among the three Chinese endemic wheat groups, a total of 10, 14 and 11 alleles at Gli-1 locus; 11, 14 and 12 alleles at Gli-2 locus; and 5, 6 and 8 alleles at Glu-1 locus were identified, respectively. Among Yunnan hulled wheat, Tibetan weedrace and Xinjiang rice wheat, the Nei's genetic variation indexes were 0.3798, 0.5625 and 0.5693, respectively. These results suggested that Tibetan weedrace and Xinjiang rice wheat had higher genetic diversity than Yunnan hulled wheat.     

青藏高原高寒草原近地表圈层N2O梯度及交换特征

深入了解N2O在不同生态系统土壤及大气中产生和交换特征对于全球气候变化研究具有重要意义.本研究重点探讨N2O在高寒草原近地表圈层中的产生及迁移过程机制.于2000年7月至2001年7月在青藏高原高寒草原地区从土壤1.5 m深到大气中32 m高度10个层次梯度进行N2O浓度变化的观测.结果显示,土壤和大气中N2O浓度均有明显的变化特征.大气中各个层次N2O的浓度都低于土壤中N2O浓度,此浓度差异直接导致了该地区高寒草原土壤向大气中排放N2O气体,其平均排放通量为0.05×10-4μmo1.m-2.s-1,但是在实验点上全年的观测中,N2O气体排放并没有表现出明显的季节性变化特征.土壤中N2O浓度随深度增加而不断升高,浓度最高值出现在1.5 m深处.进一步的分析表明,N2O浓度随深度递增主要是由环境因子中同样递增的土壤湿度所引起的.大气中不同梯度上N2O气体没有明显的浓度差异.近地表各个圈层中N2O浓度在季节上有非常相似的变化特征,即N2O高浓度均出现在入秋和深冬时节.除了N2O浓度变化在各个圈层之间显著相关以外,表层土壤中N2O浓度也与N2O排放变化有明显的相关关系,这表明浓度的差异是导致N2O气体排放变化的最直接因素.近地表土壤中N2O气体是土壤表层N2O气体排放的直接源泉,并且深层土壤中的N2O气体浓度高于浅层土壤,由此我们可以认定土壤中N2O气体通过微生物作用产生以后,由于浓度差异导致从深层土壤到浅层土壤的逐步扩散,最后经地表排放到大气当中去.     

青藏高原隆起与东亚旧石器文化的发展

近年来对青藏高原隆起的时间与幅度以及对邻近地区及全球性气候的影响等问题的认识逐渐深入。在亚洲中部隆起的巨大高原山脉,不但改变了全球的气候系统,形成东亚季风气候区,也造成中亚及邻近地区的干旱与沙漠化,在东西方之间形成天然屏障,阻碍早期人类基因与文化的交流。东亚地区古人类文化的发展历程也清楚地记录了这种情况。本文拟通过对早更新世以来东亚与西方旧石器文化关系的比较,初步探讨青藏高原隆起对东亚及整个旧大陆地区远古人类及其文化发展的深刻影响。     

我国东海赤潮原甲藻应属哪种？

阐述并讨论了中国东海长江口外经常发生的原甲藻赤潮原因种的种类认知问题．论述了自从Stein提出具齿原甲藻(Prorocendrum dentatum Stein)新种后迄今中外专家报告该种的描述及分布,并对比了具齿原甲藻与长江口的原甲藻的异同．研究证实我国东海的原甲藻与具齿原甲藻有较大的差别,主要表现在体积大小、藻体末端形态以及藻体前端突起的大小和形态等方面．本文汇集了国内外对具齿原甲藻与我国原甲藻的研究成果,对比认为。我国长江口外经常发生赤潮的原甲藻为东海原甲藻(Prorocendrum donghaiense Lu)．文中还讨论了由陆斗定发表的东海原甲藻需要补充修正的观点．在过去的数年中,我国东海长江口海域频繁爆发大面积的原甲藻赤潮,但对于赤潮原因种原甲藻(Prorocentrum)的定种问题存在两种不同的观点,一种观点认为本种是具齿原甲藻,另一种观点认为是东海原甲藻．为了阐明此种原甲藻的命名问题,于2002年11月在深圳召开了题为“我国东海赤潮原因种原甲藻分类学国际研讨会”．认为是P．dentatum的依据是长期以来国际上通常把类似我国东海的原甲藻定为P．dentatum,其根据是它的前端有突起等．而持不同观点的专家认为我国东海的这种原甲藻在细胞长度上与Stein描述的原P．dentatum差异很大,并且除少数样品末端尖伸外,大多数细胞末端是钝圆的．专家们还认为在日本、韩国等亚洲海域分布的被报告为P．dentatum的原甲藻与我国东海的此种原甲藻为同一种．综观各种观点,作者认为东海本种原甲藻应为东海原甲藻.     

黄海和东海营养盐分布及其对浮游植物的限制

根据1997～1999年黄海和东海4个季节的现场调查资料,分析探讨了黄海、东海的营养盐分布特征及其对浮游植物生长的限制状况．结果表明,在长江口以东及其东北部海域终年存在一个范围很大的营养盐高值区．分析表明,这些营养盐主要来自长江冲淡水的扩展及苏北沿岸流的输送．此外,还获得了1998年长江流域特大洪水期间,迄今被观测到的长江冲淡水中营养盐的最大扩展范围,计算并研究了黄海、东海上层水中Si／N／P比值,结果表明,黄东海上层水中Si／N比值较高,Si不会成为黄东海浮游植物生长的限制因子;但在南黄海南部尤其是西南部、东海近岸及长江口以东海域,N／P比值很高(>30),说明与一般海洋环境的情况不同,黄海、东海有很大一部分海域浮游植物的生长受磷限制,而不是受氮限制．     

Some microbiological aspects of surface and buried soils on Mt. Kenya,East Africa

When numbers of microorganisms in profiles of surface and buried horizons on Mt. Kenya were estimated by dilution plate counting they were found to be consistently lower than those from other soils in different geographical regions as determined from the literature. The lower numbers are probably characteristic of the poorly weathered Inceptisols and Entisols usually found in the alpine zone.The A horizons of the soils studied contain proportionately fewer of the total numbers of organisms in the A, B and C horizons than observed in most soils. Estimates of organic matter were positively correlated with numbers of fungi and bacteria in the A horizons. However, other factors such as severe drought, high light intensity, low temperatures, diurnal frost heaving, low pH and paucity of clay minerals may be significant factors in suppressing the more luxuriant growth of microbial populations.Organic and inorganic horizons of buried soils sometimes exhibit higher counts of microorganisms than adjacent horizons of surface soils. However, the bacteria and fungi even in deeply buried paleosols exhibit characteristics of an unspecialized heterotrophic population. Among fungi the species were obviously the same as those isolated from one or more of the overlying horizons. Taken in conjunction with other evidence from the profiles it is concluded that the microorganisms were introduced and represent a transient or non-active population. Contamination of buried organic horizons may influence the estimated age as assessed by radiocarbon dating.     

Mitochondrial DNA differentiation among East and West African Nile tilapia populations

Variation of the ND5/6 mtDNA fragment was studied in six Nile tilapia populations using PCR and RFLP analysis. The observed variation allows a strict discrimination between eastern and western African populations.