Study On Biodiversity Of Diatom In The Mainstream Of The Lower Reaches Of The Yangtze River

Diatoms are a type of unicellular eukaryotic algae with highly silicified cell walls.The species are diverse,widely distributed in different habitat.Diatoms are important primary producers in water bodies and can respond quickly to changes in the nutrient status of water bodies.They play an important role in the water ecosystem.The mainstream of the lower reaches of the Yangtze River is vast in area and has superior natural conditions,human activities have a strong influence on the natural ecosystem.At present,there is no specific report on the diatom diversity in the area.This paper systematically studies the species composition and distribution of diatoms in the mainstream of the lower reaches of the Yangtze River and enriches the species diversity of diatoms in the mainstream of the lower reaches of the Yangtze River.It provides a scientific basis for the biodiversity conservation in the Yangtze River.It is a basic data for "Biodiversity Survey and Assessment of Phytoplankton in the mainstream of the Lower Reaches of the Yangtze River" project,and provide basic data for the country to establish a database of diatom resources in the mainstream of the lower reaches of the Yangtze RiverIn October 2016,February 2017,May 2017,and August 2017,we collected samples in 10 sites,they are Hukou,Pengze-Madang,Anqing-Chizhou,Tongling,Wuhu,Nanjing,Zhenjiang,Jiangyin,Nantong and the Yangtze River Estuary area in Shanghai.Light microscopy(LM)and scanning electron microscopy(SEM)were used to systematically identified the diatom species.The main results are as follows:1.A total of 83 genera 285 species(including varieties and forma)of diatoms were found in the mainstream of the lower reaches of the Yangtze River,including 23species(including varieties)of new records in China,and 119 species(including varieties)discovered in the Yangtze River for the first time.This article describes the detailed morphological characteristics of all species,each species is described and are illustrated with light electron microscopy and some of them illustrated with scanning electron microscopy.The new records in China are as follows: Cyclotella baltica,Aulacoseira pusilla,Eunotia indica,Eunotia richbuttensis,Encyonema appalachianum,Encyonema leibleinii,Encyonema trianguliforme,Gomphonema insularum,Gomphonema variostriatum,Reimeria uniseriata,Planothidium joursacense,Neidium tenuissimum,Sellaphora subfasciata,Sellaphoraventraloconfusa,Navicula gastrum var.signata,Navicula harmoniae,Navicula melanesica,Navicula streckerae,Gyrosigma scalproides var.eximium,Amphora inariensis,Amphora indistincta,Caloneis columbiensis,Geissleria punctifera.2.Species composition of diatoms in the mainstream of the lower reaches of the Yangtze River were summarized and analyzed,which is mainly Bacillariophyceae,with 55 genera and 228 species,accounting for 80% of the total species.There are 30species(belong to 16 genera)in Coscinodiscophyceae and 27 species(belong to 12genera)in Fragilariophyceae,which account for 10.5% and 9.5% of the total species.Fragilaria,Placoneis,Cymbella,Encyonema,Gomphonema,Achnanthidium,Luticola,Neidium,Sellaphora,Pinnularia,Navicula,Amphora,Tryblionella,Nitzschia,Surirella are dominant genera which account for 51.9 % of overall species.3.According to the sampling environment,there are four main habitat types:mainstream main channel,tributary,periphery and Yangtze River Estuary.There was no significant difference in the dominant species of diatoms in the first three habitats,most of which were widely distributed freshwater species.The diatoms in the Yangtze River Estuary were affected by tide and salinity,the dominant species was low-salt wide temperature nearshore species Skeletonema costatum,and the species composition was significantly different from other regions.The species composition of diatoms has changed slightly in different seasons,and Aulacoseira granulata(including varieties and forma)have become perennial dominant species.Asterionella formosa became the dominant species in specimens collected during the winter(8-12°C),while Diatoma vulgare grew dominantly in the spring(20-26°C)specimens.They are 167 species,132 species,130 species and 170 species of diatoms were observed in spring,summer,autumn and winter.It can be seen that the species of diatoms in the spring and winter are relatively abundant than those in the summer and autumn.4.We observed many widely distributed freshwater species(in addition to the Yangtze River estuary area): Thalassiosira lacustris,Aulacoseira granulata,Cyclotella meneghiniana,Discostella stelligera,Melosira varians,Navicula capitatoradiata,Gyrosigma acuminatum,Nitzschia palea,Surirella angusta,Actinocyclus normanii and Cymatopleura solea.In the Yangtze River Estuary area,most of them are nearshore low salinity species,such as Actinoptychus annulatus,Actinoptychus undulates,Rhaphoneis rhomoides,Tabularia fasciculata,Coscinodiscus latimarginatus,Coscinodiscus oculatus,Actinocyclus normanii,Tryblioptychus cocconeiformis,Gyrosigma scalproides,Tryblionella levidensis,Nitzschia palea,Hydrosera whampoensis and Surirella fluminensis.There are some pollution indicator species,such as Nitzschia palea,Ulnaria ulna,Cymatopleura solea,Navicula cryptocephala,Aulacoseira granulata,Gomphonema parvulum,Fragilaria crotonensis,Nitzschia inconspicua and Fallacia pygmaea.