Despite two decades of research, the cause of blooms of the diatom Didymosphenia geminata remains uncertain. Blooms have been associated with low nutrient, oligotrophic streams. In this study, we used available data from across the globe and conducted experiments to determine how D. geminata responds to soluble reactive phosphorus (SRP) concentrations. Globally, D. geminata blooms have been found in streams with SRP below 11 μg P l−1. In North America, blooms only occurred at high equivalent latitudes when SRP was very low, whereas at lower latitudes blooms were observed under higher SRP concentrations. Using an in situ experiment, we found that following physical removal of D. geminata from stones, regrowth did not occur despite low SRP concentrations. In a second experiment, we found that there were no differences in D. geminata growth between a treatment which depleted SRP and a treatment which maintained elevated springtime SRP levels. These findings indicate that D. geminata blooms do not always form when SRP is low, even when cells are present. Bloom formation that is not exclusively related to low SRP suggests additional chemical or biotic factors, specific physical conditions, a seasonal timing requirement, or some combination of these with low P that are necessary to produce blooms.

中文翻译：

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在实验条件下，Didymosphenia geminata 的水华并不完全由低磷驱动

尽管进行了二十年的研究，但硅藻 Didymosphenia geminata 大量繁殖的原因仍然不确定。水华与低营养、贫营养流有关。在这项研究中，我们使用了来自全球的可用数据并进行了实验，以确定 D. geminata 如何响应可溶性活性磷 (SRP) 浓度。在全球范围内，已在 SRP 低于 11 μg P l-1 的溪流中发现 D. geminata 水华。在北美，当 SRP 非常低时，水华只发生在高等效纬度，而在低纬度地区，水华会在较高的 SRP 浓度下观察到。使用原位实验，我们发现从宝石中物理去除 D. geminata 后，尽管 SRP 浓度较低，但并未发生再生。在第二个实验中，我们发现 D 没有差异。在耗尽 SRP 的处理和保持春季 SRP 水平升高的处理之间的双生菌生长。这些发现表明，即使存在细胞，当 SRP 低时，D. geminata 开花并不总是形成。不完全与低 SRP 相关的水华形成表明额外的化学或生物因素、特定的物理条件、季节性时间要求，或这些与产生水华所必需的低 P 的某种组合。