Assessing the composition and photo-physiology of phytoplankton communities are fundamental pieces of information to understand their role in global biogeochemical cycles mediated by primary production rates in the oceans. Photo-physiological parameters, namely the maximal photochemical efficiency (F_v/F_m) and the effective absorption cross-section of Photosystem II (σ_PSII), are currently used to estimate primary production rates in the laboratory and nature, and although variable fluorescence techniques substantially expand opportunities for new measurements in both time and space, their results reflect synergies among phytoplankton composition, cell size, limiting nutrients, and light history that need to be accounted for. The current work compared the variability of F_v/F_m and σ_PSII, as well as phytoplankton groups derived by pigment-CHEMTAX analyses, at the surface and deep chlorophyll maximum (DCM) of two sections of oceanographic stations over in the productive South Atlantic Subtropical Front (STF) at 35°S of latitude, and crossing the adjacent oligotrophic waters of the South Atlantic Gyre. High chlorophyll-a concentrations were found in the STF, where the presence of cyclonic eddies displaced the pycnocline upwards, and F_v/F_m varied according to specific photo-protective mechanisms of the phytoplankton groups in the surface. In the DCM, higher F_v/F_m were related to the Chl-a synthesis, suggesting a more favorable growing condition at this layer. In the Gyre transect, F_v/F_m showed significant linear relationships with the taxonomical composition, with larger values related to the presence of Prochlorococcus and Chl b-containing green flagellates. Overall, σ_PSII varied independently from F_v/F_m but were related to the presence of diatoms and the relative proportion between Synechococcus and Prochlorococcus in the STF and Gyre, respectively. Our results encourage the development of more complex models for primary production that should include instantaneous and high-resolution fluorescence-derived parameters as proxies for phytoplankton community and physiological acclimation state.

评估浮游植物群落的组成和光生理特性是了解其在海洋初级生产力介导的全球生物地球化学循环中的作用的基本信息。光生理参数，即最大光化学效率（F _v / F _m）和光系统II的有效吸收截面（_σPSII）），目前用于估算实验室和自然界的主要生产速率，尽管可变荧光技术极大地扩展了在时间和空间上进行新测量的机会，但其结果反映了浮游植物组成，细胞大小，有限的营养物质和光照历史之间的协同作用需要考虑的。当前的工作比较了F _v / F _m和_σPSII的变异性，以及通过色素-CHEMTAX分析得出的浮游植物基团，位于生产性南大西洋副热带锋（STF）在纬度为35°的两个海洋学站点的表面和深部叶绿素最大值（DCM）处，并与南大西洋回旋区附近的贫营养水域。在STF中发现了较高的叶绿素-a浓度，其中旋风涡旋的存在使比浓菌碱向上移位，并且F _v / F _m根据表面浮游植物基团的特定光保护机理而变化。在DCM中，较高的F _v / F _m与Chl-a合成有关，表明该层的生长条件更为有利。在Gyre样条线中，F _v / F_米显示出与分类学组合物显著的线性关系，与涉及的存在较大的值原绿球藻和叶绿素b的含绿色鞭毛虫。总体而言， _σPSII的变化独立于F _v / F _m，但分别与STF和Gyre中硅藻的存在以及Synechococcus和Prochlorococcus之间的相对比例有关。我们的结果鼓励开发更复杂的初级生产模型，该模型应包括瞬时和高分辨率荧光衍生参数，作为浮游植物群落和生理适应状态的代理。