Studies On Diversity Of Phytoplankton In The North Of Lake Erhai And The Taxonomy Of Psephonema Aenigmaticum(Chlorophyta)

Lake Erhai is the second largest lake in southwestern China, and an importantdrinking water source for Dali city, Yunnan province, and used for agricultureproduces and aquaculture as well. During the past decades, the cyanobacterial bloomsoccurred frequently, leading to serious environmental issues such as the deteriorationof water quality and the imbalance of aquatic ecosystem. In the present study, weperformed investigation on the spatio-temporal dynamics of phytoplanktoncomposition and abundance, phytoplankton community structure and the waterquality in the north of Lake Erhai from April2013to March2014. The relationshipbetween environmental factors and the cyanobacterial blooms from July to Decemberin2013was also analyzed. In addition, the taxonomic study for distinguishingPsephonema aenigmaticum from Planctonema lauterbornii was conducted, andresults were shown as followings:1. A total of230phytopnakton species belonging to8phylum and101genera,were identified. Chlorophyta, Cyanophyta and Bacillariophyta were the main groups,containing110species,47species and47species, respectively. The species numbersof Euglenophyta, Pyrrophyta, Cryptophyta, Chrysophyta and Xanthophyta specieswere10,9,4,1and2, respectively.2. Phytoplankton abundances were averaged5.53×107cells/L, and higher insummer and fall than in spring and winter.3. Significant succession of phytoplankton for the year round was shown as:Diatom from January to March; Anabaena in April and June and Microcystis in Julyto November.4. The trend for the succession of dominant specie in cyanobacterial bloomsshowed that the filamentous cyanobacteria had turned into Microcystis.5. During the period of cyanobacterial blooms, the dominant species wasMicrocystis, followed by Psephonema. Correlative analysis showed that TN, TP andwater temperature were the important factors followed by change of thephytoplankton abundance, and TN was more crucial for the increase of Microcystispopulations.6. Annual variations of water quality showed that the trophic status of LakeErhai was probably transferring from mesotrophic to eutrophic, and the trophic levelswere higher in the autumn and winter than in the spring and summer.7. The four strains of Psephonema aenigmaticum and Planctonema lauterbornii were firstly isolated from Lake Erhai, encoded as CHAB5300, CHAB5302,CHAB5349and CHAB5370.8. Based on the morphological and ultrastructure characteristics betweenPsephonema aenigmaticum and Planctonema lauterbornii, the significant differenceis the cellular size.9. Based on18S rDNA gene sequences of Psephonema aenigmaticum andPlanctonema lauterbornii, it was shown that Psephonema aenigmaticum had theintrons insertion sequences, indicating that Psephonema aenigmaticum may be asubspecies of Planctonema lauterbornii.