Rising atmospheric CO₂ concentrations are predicted to have a significant impact on global phytoplankton populations. Of particular interest in freshwater systems are those species that produce toxins or impact water quality, though evidence for how these species, and many others, will respond is limited. This study investigated the effects of elevated CO₂ (1,000 ppm) relative to current atmospheric CO₂ partial pressures (400 ppm), on growth, cell size, carbon acquisition, and photophysiology of five freshwater phytoplankton species including a toxic cyanophyte, Raphidiopsis raciborskii, from Lake Wivenhoe, Australia. Effects of elevated CO₂ on growth rate varied between species; notably growth rate was considerably higher for Staurastrum sp. and significantly lower for Stichococcus sp. with a trend to lower growth rate for R. raciborskii. Surface area to volume ratio was significantly lower with elevated CO₂, for all species except Cyclotella sp. Timing of maximum cell concentrations of those genera studied in monoculture occurred in the lake in order of CO₂ affinity when free CO₂ concentrations dropped below air equilibrium. The results presented here suggest that as atmospheric levels of CO₂ rise, R. raciborskii may become less of a problem to water quality, while some species of chlorophytes may become more dominant. This has implications for stakeholders of many freshwater systems.

中文翻译：

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升高的二氧化碳对亚热带淡水湖中五种微藻的影响不同：对浮游植物物种组成的可能影响

预计大气中CO ₂浓度的上升将对全球浮游植物种群产生重大影响。在淡水系统中，特别令人关注的是那些产生毒素或影响水质的物种，尽管这些物种以及许多其他物种将如何应对的证据有限。这项研究调查了相对于当前大气CO ₂分压（400 ppm）升高的CO ₂（1,000 ppm），对包括有毒蓝藻Raphidiopsis raciborskii在内的5种淡水浮游植物的生长，细胞大小，碳吸收和光生理的影响。来自澳大利亚的Wivenhoe湖。CO ₂升高的影响物种之间的增长率不同；值得注意的是Staurastrum sp。的生长速度要高得多。而对于Stichococcus sp。则明显更低。R. raciborskii的增长率趋于降低。除Cyclotella sp。以外的所有物种，表面积与体积之比均随CO ₂升高而显着降低。当游离CO ₂浓度降至空气平衡以下时，在单培养中研究的那些属的最大细胞浓度的时间以CO ₂亲和力的顺序出现在湖中。此处显示的结果表明，随着大气中CO ₂含量的升高，R。raciborskii可能对水质的影响较小，而某些种类的绿藻可能更占优势。这对许多淡水系统的利益相关者都有影响。