Study On The Morphology,Classification And Physiology Of Skeletonema Subsalsum

Skeletonema is a worldwide distributed planktonic diatom,which blooms can lead to red-tide.In the previous studies of Skeletonema along the coastal waters of China,the researchers often focused only on the individual species Skeletonema costatum.However,there are few studies on the morphological characteristics,classification position,ecological characteristics and geographical distribution of Skeletonema in freshwater.The morphological in freshwater Skeletonema is,relatively small and difficult to distinguish under light microscope.It needs to be observed by electron microscope and combined with molecular biology,which makes it more difficult to classify freshwater Skeletonema.In recent years,when monitoring the main water bodies in Shanghai,we found that one Skeletonema sp has gradually become the dominant species.The species was isolated and purified from Dishui Lake were taken as the research object.According to the morphological characteristics under LM and SEM,combined with three kinds of molecular marker genes,it was identified as Skeletonema subsalsum.Three genes,eg,ribosomal LSU nrDNA,ITS fragments(5.8s rDNA and transcriptional spacer)and mtDNA(COXI)were used to analyze the genetic diversity and systematic.From the aspect of molecular biology to analysis the interspecific differences and systematic evolution of the genus Skeletonema in China.The most suitable molecular marker gene was analyzed for species identification of this genus.We also studied the effects of different temperature,light and salinity on the growth of S.subsalsum,and the effects of different salinity on the morphology and structure of the species.Combined with the existing research results and the studies in our laboratory,the geographical distribution of S.subsalsum was analyzed and discussed.This study provides important data for the classification,physiological characteristics and geographical distribution of the genus Skeletonema.The main results are shown as follow:1.In this study,we isolated the dominant species of Skeletonema sp.from Dishui Lake in Shanghai,and identified it as S.subsalsum by morphological and molecular methods.The main morphological characteristics of this species are different from other freshwater Skeletonema spp.:Most of the cells formed long chains and bent,rectangular in grand view,single or two chloroplast,and spacing between cells were not obvious in LM.Adjacent cells are usually close and tightly connected with processes in flattened valve faces,valve view is 3-6?m in diameter,mantle areolae were rectangular and arranged in regular pervalvar rows.The valve had 3-4 areolae in 1?m and 5-7 vertical rows of mantle areolae in 1?m.The valvocopula is narrow,more highly silicified band attached to the valve mantle.The number of processes per valve are 7-13,it is surrounded by three satellite pores,one at each corner of a triangle.2.Based on the genetic diversity and phylogenetic analysis of the three marker genes,it was found that the S.subsalsum formed a sister group with S.costatum and S.potamos.And among the three marker genes,mitochondrial coding cytochrome oxidase C(COXI)is the most suitable for interspecific differential analysis.3.The study object of this paper is quite different from most of the reports on the morphology of S.subsalsum.Therefore,different salinity gradients(0-10‰)were set up to investigate the effects of different salinity on the morphology of S.subsalsum.The results show that:In the range of 0-10‰,the cell diameter between3-6?m,the cell penetration axis becomes shorter with the increase of salinity,but the change is not obvious when the salinity increases to 2‰.With the increase of salinity(0-8‰),the supporting protruding process increased gradually,and the correlation was significant,but when the salinity was above 8‰,the length of the supporting protruding process remained basically unchanged.4.There are few studies on S.subsalsum,so it lack some physiological characteristics of this species.Therefore,the optimum growth conditions of S.subsalsum were studied in this study.The results showed that it was suitable to grow at 20-30?,high temperature(35?)has a certain inhibitory effect on its growth,but it could still grow at low temperature.It is suitable for medium-intensity illumination between 60-90?mol/(m~2·s),strong light had a certain inhibitory effect on the growth of S.subsalsum.It is suitable for growth under low salinity(0‰),with a salinity of over 10‰and almost no growth.When salinity is more than 5‰,cells can also grow,but grow slowly.