| The Yangtze River is the third longest river in the world and the "mother river" of the China.The upper and middle of the Yangtze River start from Yibin in Sichuan province and end at Hukou in Jiangxi province,with a total length of 5,459 kilometers.The area is vast,with rich resources and superior natural conditions.During our investigation,algal samples were collected in August and November 2020 and January and April 2021 from 25 sampling areas in the upper and middle reaches of the Yangtze River.The 25 sampling areas include Yibin,Jiang'an town,Luzhou,Hejiang,Jiangjin,Chongqing city,Fuling,Zhongxian,Wanzhou,Yunyang,Fengjie,Wushan,Badong,Guojiaba,Zigui,Yichang,Yidu,Jingzhou,Shishou,Yueyang,Chibi,Wuhan,Huangshi,Wukou,and Hukou.A total of 362 planktonic diatom samples were collected and more than 720 permanent seals were made.Light microscope(ZEISS Imager.A2)and scanning electron microscope(Hitachi S-4800)were used to study the planktonic diatom.On the basis of species identification,combined with the physical and chemical indicators of each sampling area,the diversity characteristics of planktonic diatoms and their correlation with environmental factors were preliminarily discussed.The main results are as follows:1.The abundance of planktonic diatom species in the upper and middle of the Yangtze River was high.A total of 355 taxa,belong to 3 classes,32 families,77 genera were identified.Twenty one taxa were newly recorded species in China and 13 undetermined species.Habitats information and morphological characteristics of each taxon was described.Light microscope photos are provided to all species.SEM pictures are given to some taxa.2.Among all the species,Coscinodiscophyceae observed 8 families,13 genera and 31 taxa,Fragilariophyceae are 41 taxa were observed in 1families,11 genera,and the remaining 238 taxa belong to the Bacillariophycidae.3.From the different collection seasons,the highest number of planktonic diatom species was observed in autumn with 276 taxa;in summer 247 taxa was observed;in winter 242 taxa was observed;the lowest number of planktonic diatom species was observed in spring with 239 taxa.Lower winter temperatures resulted in lower species richness of planktonic diatoms;The species richness increased with increasing temperature in summer,but decreased due to floods.Only 16 taxa were observed in spring;Only 21 taxa were observed in summer;Only 25 taxa were observed in autumn;and Only 16 taxa for species in winter.4.From the sampling areas,the highest number of biodiversity was observed in the Yidu area with 214 taxa;the least number of biodiversity was observed in the Chibi area with 60 taxa.Thirteen taxa were observed in all the 25 sampling areas.In addition to Yibin,Jiang ' an town,Luzhou,Chongqing,Fuling,Yunyang,Shishou,Chibi,17 sampling areas have unique distribution of planktonic diatom species.5.From the whole study basin,the biodiversity of planktonic diatoms in the upper to middle reaches of the Yangtze River showed an overall increasing trend,and the highest biodiversity was found in Yidu.Due to the confluence of tributaries and the influence of dams,the biodiversity in the middle of the Yangtze River was higher than that in the upper of the Yangtze River. |
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