The morphological response of Emiliania huxleyi to seawater carbonate chemistry changes: an inter-strain comparison

Four strains of the coccolithophore Emiliania huxleyi (RCC1212, RCC1216, RCC1238, RCC1256) were grown in dilute batch culture at four CO2 levels ranging from ~200 µatm to ~1200 µatm. Coccolith morphology was analyzed based on scanning electron micrographs. Three of the four strains did not exhibit a change in morphology over the CO2 range tested. One strain (RCC1256) displayed an increase in the percentage of malformed coccoliths with increasing CO2 concentration. We conclude that the sensitivity of the coccolith-shaping machinery to carbonate chemistry changes is strain-specific. Although it has been shown before that carbonate chemistry related changes in growth- and calcification rate are strain-specific, there seems to be no consistent correlation between coccolith morphology and growth or calcification rate. We did not observe an increase in the percentage of incomplete coccoliths in RCC1256, indicating that the coccolith-shaping machinery per se is affected by acidification and not the signalling pathway that produces the stop-signal for coccolith growth.

本研究以4株赫氏颗石藻（Emiliania huxleyi，颗石藻（coccolithophore））为研究对象，菌株编号依次为RCC1212、RCC1216、RCC1238及RCC1256，将其置于稀释分批培养体系中，在约200 µatm至1200 µatm的4个二氧化碳分压梯度下开展培养。本研究基于扫描电子显微图像（scanning electron micrographs）对颗石（coccolith）形态进行分析。结果显示，4株菌株中有3株在受试二氧化碳分压范围内未出现颗石形态的显著变化；仅菌株RCC1256的畸形颗石（malformed coccoliths）占比随二氧化碳浓度升高呈上升趋势。本研究认为，颗石成型机制（coccolith-shaping machinery）对碳酸盐化学环境变化的敏感性具有菌株特异性。尽管此前已有研究证实，碳酸盐化学环境变化对生长速率与钙化速率（calcification rate）的影响存在菌株特异性，但目前尚未发现颗石形态与生长速率或钙化速率之间存在稳定的相关性。本研究未在RCC1256中观察到未完成颗石（incomplete coccoliths）占比的上升，这表明酸化作用直接影响了颗石成型机制本身，而非调控颗石生长终止信号的信号通路。