Flow cytometric assessment of cytotype distributions within local populations of Phragmites australis (Poaceae) around Lake Biwa,the largest lake in Japan

Phragmites australis (Poaceae) is a clonal perennial that is an important component of wetland ecosystems worldwide. Using flow cytometry, we examined the cytotype distributions within five populations of P. australis located in the vicinity of Lake Biwa. As in previous reports, two ploidy levels, octoploid (2n = 8x = 96) and decaploid (2n = 10x = 120), were identified, which are assumed to be the main cytotypes around the lake. The coexistence of two cytotypes was detected in four of the five populations, suggesting the relatively common occurrence of mixed ploidy levels in the populations around Lake Biwa. Although intermingled cytotype distributions were observed in some populations, the 9x cytotype, that is, the expected outcome of inter‐cytotype crosses, was not observed, indicating limited gene flow between the two cytotypes.     

Metagenomic insights into strategies of carbon conservation and unusual sulfur biogeochemistry in a hypersaline Antarctic lake

Organic Lake is a shallow, marine-derived hypersaline lake in the Vestfold Hills, Antarctica that has the highest reported concentration of dimethylsulfide (DMS) in a natural body of water. To determine the composition and functional potential of the microbial community and learn about the unusual sulfur chemistry in Organic Lake, shotgun metagenomics was performed on size-fractionated samples collected along a depth profile. Eucaryal phytoflagellates were the main photosynthetic organisms. Bacteria were dominated by the globally distributed heterotrophic taxa Marinobacter, Roseovarius and Psychroflexus. The dominance of heterotrophic degradation, coupled with low fixation potential, indicates possible net carbon loss. However, abundant marker genes for aerobic anoxygenic phototrophy, sulfur oxidation, rhodopsins and CO oxidation were also linked to the dominant heterotrophic bacteria, and indicate the use of photo- and lithoheterotrophy as mechanisms for conserving organic carbon. Similarly, a high genetic potential for the recycling of nitrogen compounds likely functions to retain fixed nitrogen in the lake. Dimethylsulfoniopropionate (DMSP) lyase genes were abundant, indicating that DMSP is a significant carbon and energy source. Unlike marine environments, DMSP demethylases were less abundant, indicating that DMSP cleavage is the likely source of high DMS concentration. DMSP cleavage, carbon mixotrophy (photoheterotrophy and lithoheterotrophy) and nitrogen remineralization by dominant Organic Lake bacteria are potentially important adaptations to nutrient constraints. In particular, carbon mixotrophy relieves the extent of carbon oxidation for energy production, allowing more carbon to be used for biosynthetic processes. The study sheds light on how the microbial community has adapted to this unique Antarctic lake environment.     

Reproducing Authigenic Carbonate Precipitation in the Hypersaline Lake Acıgöl (Turkey) with Microbial Cultures

In the present study, laboratory precipitation experiments using similar water chemistry and two different bacterial cultures from Lake Ac?göl sediments, a hypersaline lake in Turkey, were performed to reproduce mineral assemblages similar to those found in the lake. Two different bacterial cultures induce various calcium/magnesium carbonates precipitation under all the experimental conditions (solid vs. liquid): Hydromagnesite, dypingite, huntite, monohydrocalcite, and aragonite. The geochemical program PHREEQC was used to calculate the mineral saturation indexes in the cultures and in lake water. Carbonate mineral assemblages identified in the experiments seem to be independent of the type of microorganisms but rather controlled by the chemical composition and physical conditions of the media. The relative amounts of monohydrocalcite, hydromagnesite, and dypingite are controlled by varying sulfate concentration from 0 to 56 mM. This demonstrates a kinetic effect that could similarly affect the mineral assemblage in the lake. Also the spherical morphology of hydromagnesite points to growth of these minerals under partial inhibition in the brine under high concentrations of ions and organic polymers produced by the microbial communities. As reproduced by the culture experiments, the authigenic carbonate mineral assemblage of Lake Ac?göl most likely results from interplay of ionic composition of the brine and microbial effects.     

上海滴水湖两种枝角类牧食对浮游植物群落影响的模拟研究

于2012年9月通过浮游动物添加实验,研究了大型溞(Daphnia magna)和隆腺溞(Daphnia carinata)对上海滴水湖浮游植物群落结构的影响.结果表明,实验组氨氮和可溶性活性磷浓度与空白组相比显著增加,大型溞组浮游植物密度较空白组降低了70.3％,隆腺溞组浮游植物密度较空白组降低了80.0％,叶绿素a浓度分别下降了80.4％和75.2％,叶绿素a与氨氮、可溶性活性磷呈显著相关性.浮游植物的群落结构较空白组也发生较大变化,硅藻、蓝藻和绿藻密度比例明显降低,隐藻、裸藻和甲藻在实验结束时没有检出,说明大型溞和隆线溞能有效控制水体中浮游植物密度,并能够对浮游植物群落结构产生影响.同时,附着藻类密度较空白组也有明显减少,说明大型溞和隆线溞对附着藻类也有一定的牧食作用.     

An indicator framework for assessing the technology aspect of Integrated Lake Basin Management for Lake Malawi Basin

Lake Malawi is one of the African Great Lakes and is well known for its fish biodiversity which is the greatest in the world for freshwaters. The lake basin is a valuable resource to the riparian countries. Activities associated with the derivation of the values offered by the lake basin, however, result in the generation of wastes and pollutants that also impact on the lake basin. Such anthropogenic activities within the lake basin place considerable strain on the lake system and may lead to the degradation of the lake basin. Proper application of technology can effectively supplement command-and-control measures and economic instruments for better lake basin management. Currently, no comprehensive framework exists to assess the management of the lake basin. Such a framework is necessary to guide managers and policy-makers in the formulation of management plans and strategies for the sustainable management and utilization of the lake basin. We propose an indicator framework for assessing the technology aspect of Integrated Lake Basin Management (ILBM) in the context of the Lake Malawi Basin. We further demonstrate applicability of the proposed framework through a study conducted in the Malawian side of the basin. We applied a five point Likert-type scale in our indicator assessment. Overall, our results show that the technology aspect of the management of the lake basin is weak to moderate. This threatens the sustainability of the lake especially in the areas of solid waste management, sanitation services, pollution control and protection of wetlands and lagoons which performed from very low to moderate. The major challenges are weak institutional capacity, weak regulation enforcement, and insufficient resources.     

太湖贡湖湾食物网特征研究

应用稳定性同位素技术(13C和15N)研究了太湖贡湖湾食物网特征, 结果显示由于食物来源变化多样性影响, 导致贡湖的食物网结构和营养级关系变化较为复杂, 贡湖主要生物类群13C、15N值表现出较大的种间差异。消费者13C值从摇蚊幼虫的-32.3到锯齿米虾的-22.1, 其值大小与营养级的关系没有规律性。消费者平均15N值从褶纹冠蚌的10.3到位于顶端间下鳙的19.0, 随营养级位置而升高。群落中所有种类的15N、13C值之间没有相关性(r=0.1835, P0.05), 表明该食物网是非线性食物网。研究结果验证了杂食性生物有机体普遍存在于富营养化的贡湖水域生态系统中, 且13C结果表明, 浮游植物、固着藻类以及沉水植物为贡湖食物网中大多数生物有机体的主要碳源。贡湖食物链长度为4.44营养级。     

甘肃小苏干湖盐沼湿地盐地风毛菊叶形态-光合生理特征对淹水的响应

盐沼湿地植物叶片功能性状对淹水的响应分析, 有助于探究植物叶片可塑性机制与光合生理特征间的内在关联性, 对深入理解盐沼湿地植物的生境抗逆性策略具有重要意义。根据小苏干湖湖水泛滥区静水持留时间长短分别设置: 轻度淹水区(静水持留30-90天)、中度淹水区(静水持留90-150天)、重度淹水区(静水持留150-210天) 3个试验样地, 以盐地风毛菊(Saussurea salsa)为研究对象, 研究了小苏干湖盐沼湿地盐地风毛菊叶片功能性状对淹水的响应。结果表明: 随着静水持留时间的增加, 轻度淹水区盐地风毛菊形态上采用小比叶面积(SLA)的肉质化小叶模式, 光合生理上具有高实际光合效率(Y(II))和低调节性能量耗散的量子产额(Y(NPQ))的协同变异; 重度淹水区盐地风毛菊形态和光合生理上则采用与轻度淹水区完全相反的协同变异策略; 在3个样地中, SLA与Y(II)、光化学淬灭(QP)和Y(NPQ)间均呈极显著相关关系; 叶绿素a含量和叶绿素b含量与调节性能量耗散的量子产额(Y(NO))均呈显著正相关关系。小苏干湖湖水泛滥区静水时空演变格局影响下, 盐地风毛菊种群通过改变叶面积、叶厚度和SLA等叶片形态特征, 适时调整叶片Y(II)和Y(NPQ)等光合生理特征, 实现植物叶片光合碳同化产物的收支平衡, 表现出对水盐异质性环境较强的耐受性, 反映了盐沼湿地植物在极端生存环境下的叶片可塑性和抗逆性机制。     

Responses of morphological and physiological traits to herbivory by snails of three invasive and native submerged plants

3种入侵和本地沉水植物形态和生理性状对螺类牧食的响应 沉水植物水盾草(Cabomba caroliniana)已成为中国太湖流域的优势入侵水生植物。与外来物种的原产地环境相比,引入地新环境中存在的专食性天敌较少。外来物种可能会逃避其原产地环境中的天敌牧食,又因为它们的适口性相对较差,从而导致在引入地外来物种通常比本地物种遭受的牧食者影响更低(天敌逃逸假说)。本研究的目的是比较水盾草与共生的本地沉水植物对本地牧食者的响应。我们进行了一个中宇宙尺度实验,研究了水盾草和两种共生的本地沉水植物黑藻(Hydrilla verticillata)和穗花狐尾藻(Myriophyllum spicatum)对两种本地广食性腹足纲螺类萝卜螺(Radix swinhoei)和环棱螺(Sinotaia quadrata)的牧食响应。记录了它们的形态性状指标(总生物量、冠根比和相对生长率)和生理性状指标(叶片总非结构性碳、木质素和纤维素)。研究结果表明,环棱螺对3种沉水植物性状指标的影响较少。随着本地广食性螺类萝卜螺数量的增加,黑藻和穗花狐尾藻大部分植物性状发生了改变,而水盾草的植物性状表现出相对稳定的趋势。水盾草对萝卜螺的牧食更具抵抗力,这与天敌逃逸假说的假设一致。这一发现说明牧食性螺类促进了水盾草的入侵,这可能会改变沉水植物群落中的物种组成。     

Genetic population structure as indirect measure of dispersal ability in a Lake Tanganyika cichlid

Diversification and speciation processes are influenced by intrinsic (ecological specialization, dispersal) and extrinsic (habitat structure and instability) factors, but the effect of ecological characteristics on dispersal is difficult to assess. This study uses mitochondrial control region sequences to investigate the population structure and demographic history of the endemic Lake Tanganyika cichlid Neolamprologus caudopunctatus with a preference for the rock-sand interface along two stretches of continuous, rocky shoreline, and across a sandy bay representing a potential dispersal barrier. Populations along uninterrupted habitat were not differentiated; whereas, the sandy bay separated two reciprocally monophyletic clades. The split between the two clades between 170,000 and 260,000 years BP coincides with a period of rising water level following a major lowstand, and indicates that clades remained isolated throughout subsequent lake level fluctuations. Low long-term effective population sizes were inferred from modest genetic diversity estimates, and may be due to recent population expansions starting from small population sizes 45,000–60,000 years BP. Comparisons with available data from specialized rock-dwelling species of the␣same area suggest that habitat structure and lake level fluctuations determine phylogeographic patterns on large scales, while fine-scale population structure and demography are modulated by species-specific ecologies.     

水淹频率变化对鄱阳湖增强型植被指数的影响

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。