Reversal in competitive dominance of a toxic versus non-toxic cyanobacterium in response to rising CO2.
Reversal in competitive dominance of a toxic versus non-toxic cyanobacterium in response to rising CO2.
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DOI：
10.1038/ismej.2011.28
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发表时间：
2011-09
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根据气候变化的设想，到本世纪末，大气中的二氧化碳浓度将翻一番。然而，二氧化碳浓度的上升将如何影响水生微生物群落的物种组成，在很大程度上仍然是一个悬而未决的问题。在这项研究中，我们开发了一个资源竞争模型来调查密集藻华溶解无机碳的竞争。该模型预测了水华发展过程中碳化学、pH值和光照条件的动态变化如何反馈到竞争的浮游植物物种上。我们测试的模型预测在恒化器实验与单一的培养物和混合物的有毒和无毒的淡水蓝藻铜绿微囊藻。有毒菌株能够减少溶解的CO2浓度低于无毒菌株，并成为在低CO2水平的竞争优势。相反，无毒菌株可以在较低的光照水平下生长，并在高CO2水平但低光照条件下成为竞争优势。该模型捕捉到所观察到的竞争优势的逆转，并在定量上与竞争实验的结果吻合得很好。为了评估微囊藻毒素是否可能在这种竞争优势的逆转中发挥作用，我们用野生型菌株M进行了进一步的竞争实验。铜绿假单胞菌PCC 7806及其mcyB突变体的产毒能力下降。微囊藻毒素生产的野生型有很强的选择优势，在低CO2水平，但不是在高CO2水平。因此，我们的研究结果表明，在理论和实验中，二氧化碳水平的上升可以改变有害藻华的群落组成和毒性。
Climate change scenarios predict a doubling of the atmospheric CO2 concentration by the end of this century. Yet, how rising CO2 will affect the species composition of aquatic microbial communities is still largely an open question. In this study, we develop a resource competition model to investigate competition for dissolved inorganic carbon in dense algal blooms. The model predicts how dynamic changes in carbon chemistry, pH and light conditions during bloom development feed back on competing phytoplankton species. We test the model predictions in chemostat experiments with monocultures and mixtures of a toxic and non-toxic strain of the freshwater cyanobacterium Microcystis aeruginosa. The toxic strain was able to reduce dissolved CO2 to lower concentrations than the non-toxic strain, and became dominant in competition at low CO2 levels. Conversely, the non-toxic strain could grow at lower light levels, and became dominant in competition at high CO2 levels but low light availability. The model captured the observed reversal in competitive dominance, and was quantitatively in good agreement with the results of the competition experiments. To assess whether microcystins might have a role in this reversal of competitive dominance, we performed further competition experiments with the wild-type strain M. aeruginosa PCC 7806 and its mcyB mutant impaired in microcystin production. The microcystin-producing wild type had a strong selective advantage at low CO2 levels but not at high CO2 levels. Our results thus demonstrate both in theory and experiment that rising CO2 levels can alter the community composition and toxicity of harmful algal blooms.