巢湖微囊藻毒素异构体组成的时空分布特征及影响因子

有害蓝藻释放微囊藻毒素(MCs),严重威胁饮用水源地用水安全.为了解巢湖MCs污染状况及其异构体组成对水质的影响,于2012年夏季(8月)和秋季(11月),2013年冬季(2月)和春季(5月)进行采样分析,研究了巢湖水体中胞内微囊藻毒素(IMCs)和胞外微囊藻毒素(EMCs)异构体的时空分布及其与环境因子的关系.结果发现,IMCs和EMCs的平均浓度变化范围分别为0.12～6.45μg/L和0.69～1.92μg/L.在3种常见的异构体中,MC-RR和MC-LR比例较高,MC-YR最低,MC-RR和MC-LR是巢湖水体中MCs的主要异构体类型. IMCs和EMCs的异构体浓度及其比例呈现不同的时空分布特征.微囊藻生物量、水温、总磷浓度是影响IMCs和EMCs异构体浓度及其组成变化的关键环境因子.本研究表明巢湖富营养化严重的西湖区夏季能合成更多的MC-RR异构体,而秋、冬季节偏向于释放生理毒性更强的MC-LR异构体.了解MCs异构体组成变化及其关键影响因素,有助于预测预警水体MCs污染状况和评估饮用水源地MCs风险.

水华初期蓝藻颗粒有机物在不同菌群作用下分解释放营养盐的过程研究

蓝藻水华为富营养化湖泊制造了大量有机物,这些藻源有机物的分解影响了水体中的营养盐循环。通过室内模拟附生细菌(A),附生细菌与游离细菌(AF),及附生细菌与底泥细菌(AS)三个实验组作用下蓝藻颗粒有机物(POM)在黑暗条件下长期(132天)分解过程,监测颗粒态有机碳(POC)、氮(PON)、磷(POP)、硝酸盐(NO_3~–)、磷酸盐(PO_4^(3–))、溶解性有机碳(DOC)等浓度的变化,揭示蓝藻颗粒有机物的分解和营养盐释放规律。结果表明,在整个降解过程中,叶绿素a(Chla)浓度在培养第28天时降低至最低水平,在三个实验组中Chla分解速率随时间的变化而增大,平均分解速率为:(0.15±0.06)mg/(L·d)。而POC,PON,POP的分解大致分为两个阶段,快速分解大都在28天以内,而后为缓慢降解,且分解速率明显低于Chla,平均分解速率分别为(0.03±0.03)mg/(L·d),(0.04±0.05)mg/(L·d),(0.03±0.02)mg/(L·d),且呈现随着时间变化而降低的趋势。三者之间及其在三个实验组之间的分解速率并无显著性差异。A、AF、AS三个实验组中,POC的最大分解量分别为82.30%、81.90%、63.14%;PON的最大分解量分别为92.85%、91.68%、73.27%;POP的最大分解量分别为93.50%、91.25%、70.11%,表明了POC的转化量小于PON和POP,AS实验组中POM的分解量最低,说明了底泥微生物对藻源有机物具有较低的分解量。此外,随着藻源有机物的降解,水体中NO_3~–、PO_4^(3–)、DOC的最大值出现在Chla完全降解之后,分别是初始值的2.36倍、2.13倍、2.64倍,说明了藻源颗粒有机物的分解将显著增加水体中的营养盐。

Seasonal variation of Microcystis in Lake Taihu and its relationships with environmental factors

In order to monitor the changes of Microcystis along with temporal and spatial variations, seasonal variation of Microcystis in Lake Taihu was investigated by 16S-23S rRNA internal transcribed spacer denaturing gradient gel electrophoresis （16S-23S rRNA-ITS DGGE） and microscopic evaluation. Samples were collected quarterly at four sites （River Mouth, Meiliang Bay, Cross Area, and Lake Center） from August 2006 to April 2007. Results showed that Microcystis dominated total phytoplankton abundance at the four sites in all seasons except winter. The average annual abundance of Microcystis was relatively high at River Mouth and Meiliang Bay, reaching 81.22×10^6 and 61.32×10^6 cells/L, respectively. For temporal variations, Shannon-Wiener diversity index （H＇） according to DGGE profile revealed the richness of Microcystis in summer （H＇ = 1.375±0.034） and winter （H＇ = 1.650 ±0.032） was lower than that in spring （H＇ = 2.078 ±0.031） and autumn （H＇ = 2.365 ±0.032） （P 〈 0.05）. While for spatial variations, the richness of Microcystis at River Mouth （H＇ = 2.015± 0.074） was higher than at other sites during four seasons （P 〈 0.01）. Very few differences of Microcystis diversity in the same season were observed among the other three sites （P 〉 0.05）. Canonical correspondence analysis （CCA） was performed to elucidate the relationships between Microcystis operational taxonomic units （OTUs） composition and the environmental factors. Results of CCA revealed that temperature was strongly positively correlated with the first axis （r = 0.963）, while TSS was negative correlated with the second axis （r = -0.716）. Phylogenetic tree based on the sequencing results of target bands on DGGE gel indicated that samples collected in summer and winter constituted two separated clusters.

Phylogenetic diversity and specificity of bacteria associated with Microcystis aeruginosa and other cyanobacteria

Interactions between bacteria and cyanobacteria have been suggested to have a potential to influence harmful algal bloom dynamics; however, little information on these interactions has been reported. In this study, the bacterial communities associated with five strains of Microcystis aeruginosa, three species of other Microcystis spp., and four representative species of non-Microcystis cyanobacteria were compared. Bacterial 16S rDNA fragments were amplified and separated by denaturing gradient gel electrophoresis （DGGE） followed by DNA sequence analysis. The similarities among bacterial communities associated with these cyanobacteria were compared to the digitized DGGE profiles using the cluster analyses. The bacterial community structure of all cyanobacterial cultures differed. Cluster analysis showed that the similarity values among M. aeruginosa cultures were higher than those of other cyanobacterial cultures. Sequence analysis of DGGE fragments indicated the presence of bacteria including, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Bacteroidetes and Actinobacteria in the cyanobacterial cultures. Members of the Sphingomonadales were the prevalent group among the Microcystis-associated bacteria. The results provided further evidence for species-specific associations between cyanoabcteria and heterotrophic bacteria, which are useful for understanding interactions between Microcystis and their associated bacteria.

Stocks and dynamics of particulate and dissolved organic matter in a large, shallow eutrophic lake(Taihu, China) with dense cyanobacterial blooms

Cyanobacterial blooms occur in eutrophic lakes worldwide, and greatly impair these ecosystems. To explore influences of cyanobacterial blooms on dynamics of both particulate organic matter(POM) and dissolved organic matter(DOM), which are at the base of the food chain, an investigation was conducted from December 2014 to November 2015 that included various stages of the seasonal cyanobacterial blooms(dominated by M icrocystis) in a large-shallow eutrophic Chinese lake(Taihu Lake). Data from eight sites of the lake are compiled into a representative seasonal cycle to assess general patterns of POM and DOM dynamics. Compared to December, 5-fold and 3.5-fold increases were observed in July for particulate organic carbon(POC, 3.05–15.37 mg/L) and dissolved organic carbon(DOC, 5.48–19.25 mg/L), respectively, with chlorophyll a(Chl a) concentrations varying from 8.2 to 97.7 μg/L. Approximately 40% to 76% of total organic carbon was partitioned into DOC. All C, N, and P in POM and DOC were significantly correlated with Chl a. POC:Chl a ratios were low, whereas proportions of the estimated phytoplankton-derived organic matter in total POM were high during bloom seasons. These results suggested that contributions of cyanobacterial blooms to POM and DOC varied seasonally. Seasonal average C:P ratios in POM and DOM varied from 79 to 187 and 299 to 2 175, respectively. Both peaked in July and then sharply decreased. Redundancy analysis revealed that Chl a explained most of the variations of C:N:P ratios in POM, whereas temperature was the most explanatory factor for DOM. These findings suggest that dense cyanobacterial blooms caused both C-rich POM and DOM, thereby providing clues for understanding their influence on ecosystems.

Effects of copper，manganese and pH on the growth and several enzyme activities of mycorrhizal fungus Cenococcum geophilum Fr．

he effects of various concentrations of copper,manganese and ph on the growth,protein content and several enzyme activities of mycorrhizal fungus Cenococcum geophilum Fr. Were investigated.The results showed that high concentration of copper (20 mg/L)and low ph (3.0-4.0) inhibited the mycelial growth (dry weight), however, the protein content increased or not significantly reduced in mycelia after copper or manganese was applied. The activities of acid phosphatase and α-mannosidase were induced by high concentration of Mn (200-400 mg/L);but the activities of G6PDH, MTLDH and trehalase were inhibited by high content of copper(10-20 mg/L),both of the responses of these enzymes and mycelial growth under the presence of copper were correlative each other. Measurement of these enzyme activities might therefore provide a useful criterion for the evaluation of the fungitoxicity of soil contaminated by copper.

China's lakes at present:Number,area and spatial distribution

Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM,changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules.This dataset was supported by 6843 digital raster images(1:100000 and 1:50000),a countrywide digital vector dataset(1:250000),and historical literature.Comparative data were corrected for seasonal variations using precipitation data.There are presently 2693 natural lakes in China with an area greater than 1.0 km2,excluding reservoirs.These lakes are distributed in 28 provinces,autonomous regions and municipalities and have a total area of 81414.6 km2,accounting for-0.9% of China's total land area.In the past 30 years,the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131,respectively.Conversely,243 lakes have disappeared in this time period.