The effect of nitrate and phosphate availability on Emiliania huxleyi(NZEH) physiology under different CO2 scenarios

Growth and calcification of the marine coccolithophorid Emiliania huxleyi is affected by ocean acidification and macronutrients limitation and its response varies between strains. Here we investigated the physiological performance of a highly calcified E. huxleyi strain, NZEH, in a multiparametric experiment. Cells were exposed to different CO2 levels (ranging from 250 to 1314 µatm) under three nutrient conditions [nutrient replete (R), nitrate limited (-N), and phosphate limited (-P)]. We focused on calcite and organic carbon quotas and on nitrate and phosphate utilization by analyzing the activity of nitrate reductase (NRase) and alkaline phosphatase (APase), respectively. Particulate inorganic (PIC) and organic (POC) carbon quotas increased with increasing CO2 under R conditions but a different pattern was observed under nutrient limitation. The PIC:POC ratio decreased with increasing CO2 in nutrient limited cultures. Coccolith length increased with CO2 under all nutrient conditions but the coccosphere volume varied depending on the nutrient treatment. Maximum APase activity was found at 561 matm of CO2 (pH 7.92) in -P cultures and in R conditions, NRase activity increased linearly with CO2. These results suggest that E. huxleyi's competitive ability for nutrient uptake might be altered in future high-CO2 oceans. The combined dataset will be useful in model parameterizations of the carbon cycle and ocean acidification.海洋颗石藻（coccolithophorid）赫氏球石藻（Emiliania huxleyi）的生长与钙化过程受海洋酸化与大量营养盐限制的调控，且不同菌株的响应存在显著差异。本研究通过多参数实验，探究了高钙化赫氏球石藻菌株NZEH的生理表现。实验设置了250至1314 µatm的梯度CO₂浓度，并设置三种营养盐条件：营养盐充足组（R）、硝酸盐限制组（-N）与磷酸盐限制组（-P）。本研究重点关注方解碳与有机碳配额，并分别通过检测硝酸还原酶（nitrate reductase, NRase）、碱性磷酸酶（alkaline phosphatase, APase）的活性，分析了硝酸盐与磷酸盐的利用情况。在营养盐充足条件下，颗粒无机碳（particulate inorganic carbon, PIC）与颗粒有机碳（particulate organic carbon, POC）配额随CO₂浓度升高而增加，但在营养盐限制条件下则呈现出截然不同的变化模式。在营养盐限制培养体系中，PIC:POC比值随CO₂浓度升高呈下降趋势。颗石长度在所有营养盐条件下均随CO₂浓度升高而增加，但球石囊（coccosphere）体积则因营养盐处理不同而存在差异。在磷酸盐限制培养体系中，碱性磷酸酶活性在CO₂浓度为561 µatm（pH 7.92）时达到峰值；在营养盐充足条件下，硝酸还原酶活性随CO₂浓度升高呈线性增加。上述结果表明，在未来高CO₂海洋环境中，赫氏球石藻对营养盐吸收的竞争能力可能发生改变。本组合数据集可为碳循环与海洋酸化的模型参数化提供重要支撑。