New Species Determination And Phylogeny Of A Freshwater Ulva In Shanxi Province

Ulva specimens were collected during 2007 and 2014 from Shuozhou City, Shanxi Province. In this study, freshwater Ulva specimens were observed with the light microscope (LM) and transmission electron microscope (TEM). The relationship between the freshwater Ulva species and other species belonged to genus Ulva were analyzed with bioinformatic methods. The ancestral distribution and divergence time of the genus Ulva were estimated based on tufA and 18S rDNA sequences retrieved from GenBank. The results of this study are showed below:1. The Ulva specimen collected from Shuozhou is obviously different from U. intestinalis and U. prolifera, which had been found living in freshwater of China. The Ulva specimen collected from Shuozhou is characterized by abundant spinal branches in both the specimen and U. prolifera (vs. simply or rarely branched from the very base in U. intestinalis). The cell walls are not thicker on the internal surface of the thallus in transverse section in both the specimen and U. prolifera (vs. generally thickened internally in U. intestinalis). The cell dimension of Shuozhou Ulva specimen is a little bigger than U. intestinalis and U. prolifera. This freshwater Ulva specimen was named as Ulva shanxiensis L. Chen, J. Feng & S. L. Xie. At the beginning of growth process, a bigger cell and a smaller cell were observed. The TEM observation showed there were several pyrenoids in the cell, but no mitochondrion was observed during our study.2. The taxonomic position of U. shanxiensis and other taxa in Ulva was studied by phylogenetic trees reconstruction based on several molecular markers. The phylogenetic trees illustrated that this new species is different from the other taxa of Ulva and the results support the establishment of this new species. We also found that Ulva and Enteromorpha were not separated distinctively and supported the combination of these two genera.3. The MRCA of Ulva lived in ancient Asia, ancient North America, ancient Europe and ancient Oceania. The modern Ulva ditrbution was formed by several dispersal events. Seven fossil calibrations of Ulvophyceae were selected and results exhibited the TMRCA of Ulva was between 149 Mya-233 My a. It suggested that the freshwater Ulva was the relict plant of ancient marine species.4. During the field collection of Uva specimens, we also studied the flora of some sampling sites. The algae flora in Saihanwula Nature Reserve was studied in 2009. The results showed that the dominant phyla were Bacillariophyta and Chlorophyta. It revealed that species composition of the same waterbody showed a high similarity, but species composition of the different waterbody showed a greater difference. Indicator algae analysis represented that the overall water quality was good. Most of the waterbody were β-mesosaprobic zones. But it still needed better protection of the waterbody and algae diversity in the nature reserve.The freshwater Ulva is rarely found in natural inland waterbody. Its survival had been affected by the environment pollution and the over-exploitation of freshwater resources. Therefore, freshwater Ulva species should be investigated and studied without delay, which have important practical meaning in the biodiversity protection and development.