Taxonomy Of Monoraphid Diatoms In Southwestern Sichuan, China

Monoraphid diatoms are single-cell eukaryotes.They are often single cells or a population connected by several cells.There are two valves: one valve with a raphe,another valve without raphe.Monoraphid diatoms are diverse and widely distributed.Diatoms are sensitive to changes in the environment,so they can be used as indicators of the health of aquatic ecosystems.However,since this group is very small,most species are 10-20 μm,so they are difficult to observe and identify.Few systematically studies of freshwater Monoraphid diatoms were carried in China.The terrain of southwestern Sichuan is ups and downs,and the climate is complex and changeable.There are abundant resources in this region.This thesis systematically studies species composition and distribution in southwestern Sichuan,enriches the biodiversity of the monoraphid diatoms,and provides important information for the preparation of "Flora Algarum Sinicarum Aquae Dulcis-Bacillariophyta".In August 2015 and May 2018,we collected diatom samples from different habitats in Ganzi Tibetan Autonomous Prefecture and Aba Tibetan and Qiang Autonomous Prefecture in southwestern Sichuan,including swamps,mountain lakes,rivers,cold springs,ponds,streams,hot springs,surface seepage water,waterfalls,temporary water bodies,etc.,a total of 306 samples were collected,and monoraphid diatoms were studied by light microscopy(LM)and scanning electron microscopy(SEM).The main results are as follows:1.In the samples of southwestern Sichuan,a total of 77 species and 6 varieties belong to 3 families,11 genera were identified,including 1 species in Achnanthaceae,9 genera 73 species and 3 varieties in Achnanthidiaceae,and 1 genus 3 species 3 varieties in Cocconeidaceae.The morphological characteristics of each species are described in detail,and the habitat information of each species is given.All species have LM images,and some species have SEM images.We also provided the key to genera.2.A total of 7 new species were found in southwestern Sichuan: Achnanthidium ludingensis sp.nov.,Eucocconeis lanceolatum sp.nov.,Eucocconeis rectangularis sp.nov.,Platessa mugecuonsis sp.nov.,Platessa qisensis sp.nov.,Psammothidium undulatum sp.nov.and Psammothidium sichuanense sp.nov.27 species of China new records are found: including Achnanthidium 6 species,Eucocconeis 1 species,Psammothidium 10 species,Planothidium 7 species 2 varieties and Cocconeis 1 varieties.3.In this area,the main genera are Achnanthidium(23 species),Psammothidium(20 species)and Planothidium(15 species).Species diversity and species composition of Monoraphid diatoms are significant differences in different water types.Among the mountain lakes and cold springs,species diversity is higher and the dominant populations are high;the number of species in rivers,marshes,ponds,hot springs and other habitats is less,and there are few or no obvious dominant populations;In waterfalls,underground seepage water and temporary water bodies,the number of species and dominant groups are the least.Meanwhile,most of the species in the area are indicative of the clean water,and a small number of types of pollution tolerant are also found,indicating that the water environment in the area is generally well,but water bodies have been polluted in some areas.