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Ulvella species are widely distributed in ocean and freshwater habitats and from high latitudes to the tropics. However, no species of this genus have been found in the Qinghai–Tibetan Plateau. In the present study, five rock specimens were collected from the bottom of Qinghai Lake at a depth of about 15–28 m, from which three unialgal strains were isolated. These strains were characterized by prostrate pseudoparenchyma, irregular or radial branch filaments, and mono- or polystromatic discs or rosettes formed by consecutive filaments, with thalli that can grow up to 180 um in length, suggesting that they may be Ulvella species. Phylogenetic analysis based on 18S rDNA and tufA cpDNA sequences revealed that the isolates formed a strong branch among other Ulvella species and were closely related to Ulvella leptochaete and Ulvellawaernii. This result was also confirmed by neighbor-joining tree inference based on ITS2 secondary structure. Unlike other members of Ulvella, the isolated strain was characterized by its unique habitat, field morphology of thallus, size of vegetative cells, and number of pyrenoids. Based on these morphological differences, the phylogenetic analysis, and the comparison of ITS2 secondary structure with relative species, the strain isolated in this study was proposed to be a novel Ulvella sp. The alga was found on the bottom of brackish lakes on the Qinghai–Tibetan Plateau, which meant that our sampling range needed to be expanded further. [ABSTRACT FROM AUTHOR]

Massive Cladophora growth was reported half a century ago around Birds Island in Qinghai Lake, and in 2015, Cladophora populations have rebloomed and have formed green "meadows," with areas up to thousands of hectares. The present study investigated the distribution and biomass of Cladophora in Qinghai Lake and found that two key factors contribute to Cladophora blooming. First, recent climate change, especially increased precipitation, has induced the expansion of the lake's area, and the submerged grassland around Birds Island has provided a plethora of grass stems on which Cladophora can attach and twine. In addition, the submerged grasslands are covered with less than 1 m of water, which allows enough sunlight to support the growth of Cladophora on available substrates. Second, the submerged grassland may function as a key source of nutrients, especially phosphate. A large number of migratory birds live in these area for very long times, which lead to higher phosphorus content due to the accumulated birds dropping. Thus, the high phosphate level further exacerbates the massive growth. Future studies should investigate the functions of Cladophora in the nutrient cycling of submerged areas, and the improvement of methods for removing Cladophora biomass. [ABSTRACT FROM AUTHOR]