Microalgal range expansions are increasing in frequency and magnitude but generally remain unnoticed until mass development occurs. Gonyostomum semen is a freshwater raphidophyte that causes nuisance blooms in lakes and has recently expanded its distribution across Europe. G. semen was considered to mainly occur in humic lakes in the boreal region but is now found in high density also in other freshwater habitats on a larger geographic scale with growing incidence. In this study, we focused on which environmental factors limit its expansion. Our hypothesis was that G. semen occurs in many different lake types, except for high alkalinity lakes, in which high pH in combination with high calcium concentration would inhibit its growth. Results from our field study illustrate the environmental heterogeneity of G. semen bloom sites across Europe and the United States. Nevertheless, none of these sites combined high pH and high calcium concentration. In a mesocosm study, as well as a laboratory experiment, we further demonstrated that growth of G. semen is inhibited in conditions combining both high pH and high calcium concentration. We also discuss the function of Sphagnum peat mosses in rendering an alkaline habitat suitable to G. semen growth. Our study highlights that high alkalinity environments act as a major colonization barrier to G. semen. While this finding explains which environmental filters limit G. semen distribution it also helps in understanding its current expansion. With globally decreasing calcium concentrations in freshwater ecosystems, new habitats have and will become conducive to G. semen growth.

中文翻译：

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钙和 pH 值相互作用限制了有害微藻的水华形成和扩张

微藻范围扩张的频率和幅度正在增加，但在大规模发展之前通常不会被注意到。Gonyostomum semen是一种淡水藻类植物，会导致湖泊中的水华滋生，最近已将其分布扩展到整个欧洲。G. semen被认为主要出现在北方地区的腐殖质湖中，但现在在更大地理范围内的其他淡水栖息地中也发现了高密度，并且发病率不断增加。在这项研究中，我们关注哪些环境因素限制了其扩张。我们的假设是G. semen发生在许多不同的湖泊类型中，但高碱度湖泊除外，在这些湖泊中，高 pH 值和高钙浓度会抑制其生长。我们的实地研究结果说明了欧洲和美国G. semen开花地点的环境异质性。然而，这些位点都没有结合高 pH 值和高钙浓度。在一项中胚层研究以及一项实验室实验中，我们进一步证明，在结合高 pH 值和高钙浓度的条件下，G. 精液的生长受到抑制。我们还讨论的功能泥炭渲染适合碱性栖息地的泥炭苔藓G.精液生长。我们的研究强调，高碱度环境是G. semen的主要定植屏障。虽然这一发现解释了哪些环境过滤器限制了G. 精液的分布，但也有助于了解其当前的扩张。随着全球淡水生态系统中钙浓度的下降，新的栖息地已经并将变得有利于G. semen 的生长。