Data_sheet_1_Nitrogen Limitation Enhanced Calcification and Sinking Rate in the Coccolithophorid Gephyrocapsa oceanica Along With Its Growth Being Reduced.docx

Phytoplankton are exposed to different concentrations of nutrients in different waters along with changing light levels during diurnal and seasonal cycles. We grew the coccolithophorid Gephyrocapsa oceanica semi-continuously at different nitrate levels under indoor low and outdoor high light conditions, and found that reduced nitrate availability significantly increased its production of particulate inorganic carbon (PIC), with its growth being reduced. High light treatment suppressed the growth of nitrate-limited cells and their efficiency of N assimilation by up to 63% compared to low light treatment. The combination of high light and nitrate limitation increased contents of PIC per cell due to sustained photochemical energy transfer, resulting in faster sinking rates by up to 82% in comparison with nitrate-repleted cells. Additionally, the sinking rates were positively correlated with ratios of PIC to particulate organic carbon (POC). These results imply that coccolithophores distributed in oligotrophic waters could be more effective as the ballast in aggregates, facilitating particulate organic carbon flux to deeper waters.

浮游植物在不同水域会接触到不同浓度的营养盐，同时在昼夜与季节周期中还会经历光照水平的变化。本研究针对颗石藻（coccolithophorid）物种大洋桥石藻（Gephyrocapsa oceanica）开展培养实验：在室内低光照与室外高光照条件下，设置不同硝酸盐浓度进行半连续培养。结果发现，硝酸盐可利用性降低会显著提升该藻的颗粒无机碳（PIC）合成量，同时抑制其生长。与低光照处理组相比，高光照处理会抑制硝酸盐限制细胞的生长，并使其氮同化效率最高下降63%。高光照与硝酸盐限制的共同作用，会因光化学能量传递持续进行而提升单位细胞的颗粒无机碳含量，最终导致细胞沉降速率较硝酸盐充足组最高提升82%。此外，细胞沉降速率与颗粒无机碳/颗粒有机碳（POC）比值呈显著正相关。本研究结果表明，栖息于寡营养水域（oligotrophic waters）的颗石藻可作为海洋聚集体中的有效压载物，促进颗粒有机碳向深海的输送通量。