颗石藻钙化作用对多重环境变化的响应及其机制

In the ocean, change of one environmental factor may lead to changes of other multiple environmental factors, and responses of physiological rates of phytoplankton to one factor can be modulated by other factors. Thus, it is necessary to study effects of multiple environmental factors on phytoplankton. This project will investigate response of calcification rate of phytoplankton community to temperature, CO2 level, light intensity, dissolved inorganic nitrogen and phosphate concentrations in shipboard incubation. Six bottles for ambient temperature treatment were put into one deck incubator bathed with flowing surface seawater. Six bottles for the elevated temperature treatment were put into another deck incubator with an auto-temperature control system which fitted with two circulating coolers during the day, and heated at night. pH of seawater with high CO2 level was adjusted by adding the saturated CO2 seawater, and were 0.4 lower than the in situ pH of seawater with low CO2 level. Differential levels of incident solar radiation were achieved by neutral density screens. Phytoplankton community with high cell abundance of coccolithophores was collected at different stations with different nutrient concentrations. Difference between total particulate carbon production rate and particulate organic carbon production rate was considered to be calcification rate of phytoplankton community. To investigate the mechanisms behind the physiological process in laboratory, this project will study interactive effects of temperature, CO2 level, light intensity, dissolved inorganic nitrogen and phosphate concentrations on carbon-use-efficiency in the coccolithophore Emiliania huxleyi, which was easily found in East China Sea and South China Sea. In laboratory, E. huxleyi was cultured in an ‘environmental cluster’, which incorporates key environmental factors. Then, factors were sequentially changed in consecutive incubations. This study will provide important information and improve our understanding on responses of physiological rates of calcifying microalgae to climate change and the mechanisms behind the physiological processes.

在海洋环境中一个环境因子变化可能引起其他多个环境因子改变；并且单个环境因子变化对浮游植物生理特征的影响受多个环境因子变化的调控，因此有必要研究多重环境因子同时变化对浮游植物生理特征的相互影响。本项目通过航次培养实验研究原位浮游植物群落钙化速率对温度、CO2浓度、光强、无机氮和无机磷浓度的响应特征。低温由流动的表层海水控制，高温用白天冷却，晚上加热培养水浴的方法控制；培养液的CO2浓度通过添加饱和CO2海水降低其pH值来调控；利用中性网包裹培养瓶使藻细胞接受到不同光强；选取颗石藻细胞丰度高的不同站点培养浮游植物群落。在实验室内本项目选取我国海域常见的赫氏颗石藻，通过多批次培养实验，每一批实验改变一个环境因子，逐步叠加改变多个环境因子，研究温度、CO2浓度、光强、无机氮和无机磷浓度对藻细胞利用无机碳效率的相互影响。该研究结果为评估气候变化对微型钙化藻生理特征的影响及其机制提供理论依据。

气候变化和人类活动对海洋生态系统造成重大影响。本项目研究了多重环境因子变化对海洋赫氏颗石藻光合固碳和钙化作用的相互影响及其机制。高浓度CO2和低浓度无机磷主导增加赫氏颗石藻的光合固碳速率，低浓度无机氮和无机磷协同增加细胞钙化速率。在未来高浓度CO2，高温，高光强和低浓度营养盐的海洋环境下，赫氏颗石藻的生长速率显著降低，但是它们的光合固碳和钙化速率会增加。在高浓度CO2条件下，低浓度无机氮和无机磷降低细胞达到最大电子传递速率的饱和光强。在营养盐限制条件下，最大电子传递速率的饱和光强小于光合固碳和钙化速率的饱和光强。这些结果说明：为了适应营养盐限制和高浓度CO2，赫氏颗石藻降低达到最大光合固碳和钙化速率的饱和光强，这也是微藻适应高浓度CO2、高光强和低浓度营养盐的光生理策略。. 该项目进一步阐明海洋赫氏颗石藻光合固碳响应全球气候变化的生化机理。研究结果显示：与当前海洋CO2浓度相比，海洋酸化增加赫氏颗石藻糖类含量，对蛋白质含量没有显著影响。在高pH值条件下，高浓度溶解无机碳(DIC)显著增加细胞蛋白质和糖类含量。低pH值抵消了高浓度DIC对蛋白质和糖类含量的正面效应。当光强、pH值和CO2浓度分别增加时，核糖核酸与颗粒有机碳的比值(RNA:POC)随生长速率增加而增加；当温度升高时，RNA:POC比值随生长速率增加而下降。当温度、pH值和CO2浓度分别增加时，蛋白质与颗粒有机碳的比值(Protein:POC)随生长速率增加而增加；当光强和CO2浓度分别增加时，糖类与颗粒有机碳的比值(Carbohydrate:POC)随生长速率增加而增加。这些结果说明：为了适应不同海洋环境条件，赫氏颗石藻细胞内RNA、蛋白质和糖类含量呈现相反趋势，进而导致细胞碳：氮：磷比值呈现不同趋势。通过2019年春季和夏季航次采样，及收集2002–2019年台湾海峡赤潮暴发时的甲藻优势种及温度和盐度，我们提出：当台湾海峡海水温度为17–23oC，盐度为29–33‰，无机氮浓度大于2 μmol L–1时，甲藻更容易暴发赤潮。