中国淡水水体常见束丝藻种类的形态及生理特性研究

束丝藻(Aphanizomenon Morr.ex Born.et Flah)是我国水华蓝藻的重要种类,由其产生的束丝藻水华已经引起了许多的环境问题。水华束丝藻、柔细束丝藻和依沙束丝藻是我国淡水水体常见的三种束丝藻种类,然而,国内外对它们的生理学研究却相对较少。基此,文章对水华束丝藻、柔细束丝藻和依沙束丝藻的形态特性、色素含量、生长及光合作用进行了比较研究,结果表明丝状体的营养细胞、异形胞和厚壁孢子的长宽比具有一定的差异性,揭示了厚壁孢子的长宽比可作为三种束丝藻分类的一个参数;同时,种间的差异性也体现在三种束丝藻的生理特性上,相比水华束丝藻和依沙束丝藻,柔细束丝藻的藻蓝素含量较高,而叶绿素a、类胡萝卜素含量、最大光合作用(Pm)、表观光合作用效率(α)和最大电子传递速率(ETRmax)显著偏低。此外,水华束丝藻和依沙束丝藻生理特性基本一致,表明了形态不同的三种束丝藻在生理上可被分为两种类型,暗示了依沙束丝藻可能具有像水华束丝藻一样形成水华的生理潜能且由于它的产毒性所以应该倍加关注。

MORPHOLOGICAL AND PHYSIOLOGICAL CHARACTERISTICS AND COMMON APHANIZOMENON TYPES IN CHINESE WATER BODIES

Aphanizomenon has been widely reported in many freshwater bodies,and was regarded as one of important bloom-forming cyanobacterial strains.Owing to its effect,directly or indirectly,to animals and human beings,great attention has been focused on the formation mechanism by researchers in areas such as,aquatic ecology,phycology,environmental science,and so on.In China,Aphanizomenon bloom has resulted in many environmental and ecological problems.As already illustrated,bloom-forming cyanobacteria has developed some sound ecological strategies to form water bloom with a series of special physiological mechanisms and adaptation characters during evolution.However,the physiological mechanisms and adaptation characters in Aphanizomenon remain largely unknown.Previous study in our laboratory had shown that three types of Aphanizomenon,A.flos-aquae,A.gracile and A.issatschenkoi,were the most common strains in Chinese freshwater bodies.Due to the limitation of samples and knowledge,however,the physiological characters were not compared in the three-type strains so far.Therefore,in order to further explore their knowledge and investigate the bloom-forming mechanism in Aphanizomenon,in the present study,their morphological and physiological characteristics,including the ratio of length and width in vegetative cell,heterocyst and akinete,growth rate,pigment composition,photosynthetic O2evolution,and the electron transport rate(ETR),were compared in A.flos-aquae,A.gracile and A.issatschenkoi.The results indicated that some morphological differences were found in the frequency distributions for length/width ratios of vegetative cells,heterocyst,and akinetes.Among them,the most significant difference was found in the akinetes,suggesting that the length/ width ratios of akinetes could be regarded as a taxonomic unit in the genus Aphanizomenon.Moreover,physiological differences were also showed in three types of Aphanizomenon.Compared with the strains of A.flos-aquae and A.issatschenkoi,the strains of A.gracile displayed higher PC contents.However,the strains of A.gracile showed significantly lower chlorophyll α,carotenoid contents,maximum photosynthesis(Pm),apparent photosynthetic efficiency(α),and maximal electron transport rates(ETRmax) in comparison with the other strains of Aphanizomenon.It suggested that the strain of A.gracile showed lower competitive abilities in photosynthesis when compared with the strains of A.flos-aquae and A.issatschenkoi.In addition,similar physiological features,such as the value of Pm and ETRmax,pigment contents and specific growth rate(μ),were found in A.flos-aquae and A.issatschenkoi.These data suggested that the three morphological strains of Aphanizomenon could be divided into two types based on their physiological characterizations,namely,A.gracile-type and A.flos-aquae/issatschenkoi-type,and indicated that the strains of A.issatschenkoi might be potential bloom-formation strains as the same as the strains of A.flos-aquae and must be played a considerate attention due to its toxicity.