DataSheet_1_Quantifying Per-Cell Chlorophyll a in Natural Picophytoplankton Populations Using Fluorescence-Activated Cell Sorting.csv

Marine phytoplankton play a central role in global biogeochemical cycling, carbon export, and the overall functioning of marine ecosystems. While chlorophyll a (Chl a) is widely used as a proxy for phytoplankton biomass, identifying the proportion of Chl a attributable to different phytoplankton groups remains a major challenge in oceanography, especially for the picophytoplankton groups that often represent the majority of phytoplankton biomass in the open ocean. We describe a method for measuring picophytoplankton per-cell Chl a in field samples using fluorescence-activated cell sorting followed by solvent-based Chl a extraction and fluorescence quantification. Applying this method to surface samples from the Gulf of Mexico, we determined per-cell Chl a to be 0.24 ± 0.07, 0.6 ± 0.33, and 26.36 ± 20.9 fg Chl a cell-1 for Prochlorococcus, Synechococcus, and PPE, respectively (mean ± SD). Measurements of per-cell Chl a using this method are precise to within 1.7, 2.1, and 3.1% for Prochlorococcus, Synechococcus, and PPE, respectively. We demonstrate that this approach can be used to obtain estimates of group-specific Chl a for Prochlorococcus, Synechococcus, and picophytoeukaryotes, the latter two of which cannot be captured by existing methods. We also demonstrate that measurements of per-cell Chl a made using this method in field samples are sufficiently precise to capture relationships between per-cell Chl a and cytometer red fluorescence, providing a bridge between biomass estimates from cell counts and bulk measurements of total Chl a.

海洋浮游植物在全球生物地球化学循环、碳输出以及海洋生态系统整体功能中扮演着核心角色。尽管叶绿素a（Chl a）被广泛用作浮游植物生物量的替代指标，但确定不同浮游植物群体中Chl a的比例仍然是全球海洋学领域的一大挑战，尤其是对于常常代表开阔海洋中浮游植物生物量大多数的极微浮游植物群体。本文介绍了一种通过荧光激活细胞分离技术，随后采用溶剂提取和荧光定量方法来测量现场样品中极微浮游植物每细胞Chl a含量的方法。将该法应用于墨西哥湾表层样品，我们测定了三种浮游植物群体——原甲藻、拟球藻和PPE的每细胞Chl a分别为0.24 ± 0.07、0.6 ± 0.33和26.36 ± 20.9 fg Chl a细胞-1（平均值 ± 标准差）。使用此法对每细胞Chl a的测量，对于原甲藻、拟球藻和PPE，分别精确到1.7%、2.1%和3.1%。我们证实，该方法可用于获取原甲藻、拟球藻和极微真核生物的群体特异性Chl a估计值，后两者现有方法无法捕捉。此外，我们还证明，使用此法在实地样品中进行的每细胞Chl a测量足够精确，能够捕捉到每细胞Chl a与细胞计数器红色荧光之间的关系，从而在基于细胞计数的生物量估计值与总Chl a的大量测量之间架起一座桥梁。