State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China; College of Environmental Science and Engineering, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, China.
State Key Laboratory of Marine Environmental Science, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China; Co-Innovation Center of Jiangsu Marine Bio-industry Technology, Jiangsu Ocean University, Lianyungang 222005, China.
J Photochem Photobiol B. 2021 Apr;217:112145. doi: 10.1016/j.jphotobiol.2021.112145. Epub 2021 Feb 2.
Photophysiological responses of phytoplankton to changing multiple environmental drivers are essential in understanding and predicting ecological consequences of ocean climate changes. In this study, we investigated the combined effects of two CO levels (410 and 925 μatm) and five light intensities (80 to 480 μmol photons m s) on cellular pigments contents, photosynthesis and calcification of the coccolithophore Emiliania huxleyi grown under nutrient replete and limited conditions, respectively. Our results showed that high light intensity, high CO level and nitrate limitation acted synergistically to reduce cellular chlorophyll a and carotenoid contents. Nitrate limitation predominantly enhanced calcification rate; phosphate limitation predominantly reduced photosynthetic carbon fixation rate, with larger extent of the reduction under higher levels of CO and light. Reduced availability of both nitrate and phosphate under the elevated CO concentration decreased saturating light levels for the cells to achieve the maximal relative electron transport rate (rETR). Light-saturating levels for rETR were lower than that for photosynthetic and calcification rates under the nutrient limitation. Regardless of the culture conditions, rETR under growth light levels correlated linearly and positively with measured photosynthetic and calcification rates. Our findings imply that E. huxleyi cells acclimated to macro-nutrient limitation and elevated CO concentration decreased their light requirement to achieve the maximal electron transport, photosynthetic and calcification rates, indicating a photophysiological strategy to cope with CO rise/pH drop in shoaled upper mixing layer above the thermocline where the microalgal cells are exposed to increased levels of light and decreased levels of nutrients.
浮游植物对不断变化的多种环境驱动因素的光生理响应对于理解和预测海洋气候变化的生态后果至关重要。在这项研究中，我们研究了两种 CO 水平（410 和 925 μatm）和五种光强（80 到 480 μmol 光子 m⁻² s⁻¹）对营养充足和有限条件下分别生长的颗石藻 Emiliania huxleyi 细胞色素含量、光合作用和钙化的综合影响。我们的结果表明，高光强、高 CO 水平和硝酸盐限制协同作用降低了细胞叶绿素 a 和类胡萝卜素含量。硝酸盐限制主要增强钙化速率；磷酸盐限制主要降低光合碳固定速率，在 CO 和光强度较高时，降低幅度更大。在升高的 CO 浓度下，硝酸盐和磷酸盐的可用性降低，降低了细胞达到最大相对电子传递速率（rETR）所需的饱和光水平。在营养限制下，rETR 的光饱和水平低于光合作用和钙化率。无论培养条件如何，生长光水平下的 rETR 与测量的光合作用和钙化率呈线性正相关。我们的研究结果表明，适应宏量营养限制和升高 CO 浓度的 E. huxleyi 细胞降低了其对达到最大电子传递、光合作用和钙化速率的光需求，这表明一种光生理策略来应对上层混合层中 CO 上升/pH 下降，在那里微藻细胞暴露在更高水平的光和更低水平的营养物质中。
