Abstract: Our knowledge of the processes involved in speciation of microalgae remains highly limited. In the present study, we investigated a potential role of ecological speciation processes in diversification of the filamentous green alga Klebsormidium. We examined 12 strains representing four different genotypes. The strains were collected from sandstone and limestone rocks and were cultivated at five different pH levels ranging from pH 4 to pH 8. We determined the responses of the 12 strains to the experimental pH conditions by (1) measuring the effective quantum yield of photosystem II, and (2) determining the growth rates after cultivation at different pH levels. Strong differences were found between the results obtained by these two methods. Direct counting of cells revealed a strong ecological differentiation of strains of Klebsormidium isolated from different substrate types. Strains isolated from limestone showed the highest growth rates at higher pH levels; whereas, the strains isolated from sandstone exhibited two distinct growth responses with optima at pH 5 and 6, respectively. In contrast, the effective quantum yield of photosystem II was always down-regulated at lower pH values, probably due to dissolved inorganic carbon limitation. In general, we determined distinct ecophysiological differentiation among distantly and closely related lineages, thereby corroborating our hypothesis that the sympatric speciation of terrestrial algae is driven by ecological divergence. We clearly showed that pH is a critical ecological factor that influences the diversity of autotrophic protists in terrestrial habitats.

中文翻译：

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底物和 pH 对陆生藻类 Klebsormidium（Klebsormidiales，Streptophyta）多样性的影响：同域物种形成的潜在重要因素


摘要：我们对微藻物种形成过程的了解仍然非常有限。在本研究中，我们研究了生态物种形成过程在丝状绿藻 Klebsormidium 多样化中的潜在作用。我们检查了代表四种不同基因型的 12 株菌株。这些菌株是从砂岩和石灰岩岩石中收集的，并在 pH 4 至 pH 8 的五种不同 pH 水平下培养。我们通过 (1) 测量光系统 II 的有效量子产率来确定 12 种菌株对实验 pH 条件的响应，(2) 确定在不同 pH 水平下培养后的生长速率。这两种方法获得的结果之间存在很大差异。细胞的直接计数揭示了从不同底物类型中分离出的克雷伯索米氏菌菌株的强烈生态分化。从石灰石中分离出的菌株在 pH 值较高的情况下表现出最高的生长率；然而，从砂岩中分离出的菌株表现出两种不同的生长反应，最佳pH值分别为5和6。相比之下，光系统 II 的有效量子产率在较低 pH 值下总是下调，这可能是由于溶解的无机碳的限制。总的来说，我们确定了远缘和密切相关的谱系之间存在明显的生态生理分化，从而证实了我们的假设，即陆地藻类的同域物种形成是由生态分化驱动的。我们清楚地表明，pH 值是影响陆地生境中自养原生生物多样性的一个关键生态因素。