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

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.本研究选取4株赫氏颗石藻（Emiliania huxleyi，隶属于颗石藻（coccolithophore））菌株（RCC1212、RCC1216、RCC1238、RCC1256），采用稀释分批培养体系，在约200 µatm至约1200 µatm的4个CO2分压梯度下进行培养。基于扫描电子显微照片（scanning electron micrographs）对颗石（coccolith）的形态特征进行分析。结果表明，在测试的CO2分压范围内，4株菌株中有3株未出现形态变化；而菌株RCC1256的畸形颗石（malformed coccoliths）占比随CO2浓度升高显著增加。本研究得出结论：颗石成型机制（coccolith-shaping machinery）对碳酸盐化学变化的敏感性具有菌株特异性。尽管此前已有研究证实，碳酸盐化学变化引发的生长速率与钙化速率（calcification rate）的改变同样存在菌株特异性，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一致的相关性。本研究未在RCC1256中观察到未完成颗石（incomplete coccoliths）占比的升高，这表明酸化胁迫主要影响的是颗石成型机制本身，而非调控颗石生长终止信号的信号通路（signalling pathway）。