Light drives phytoplankton photosynthesis, so phytoplankton in their living habitats must exploit variable light levels and exposure durations, depending upon seasons, latitudes, depths and mixing events. Comparative growth, physiology and biochemical compositions were explored for the small Alexnadrium minutum (˜40 μm³ biovolume) and large Alexandrium catenella (˜9300 μm³ biovolume), globally wide spread coastal toxic red tide dinoflagellates, responding to a matrix of photoperiods (Light:Dark, 8:16, 16:8 and 24:0) and growth light irradiances. Smaller A. minutum grew faster under shorter photoperiods across growth light levels, while larger A. catenella grew fastest under longer photoperiods at the lowest applied light level. Photosystem II function responded largely to the instantaneous growth light level across photoperiod lengths, while the cell biovolume-based respiration, antioxidant capacity as well as cell composition responded more to photoperiod duration than to light level. These complex photophysiological responses resolved into linear correlations between growth rate versus cellular antioxidant activity and versus dark respiration, indicating that respiration energizes cellular antioxidant systems to benefit the growth of the cells. These results show the growth responses of Alexandrium species to light levels across photoperiods vary with species, and possibly with cell size. Together with previous results this puts a note of caution on meta-analytical extrapolations of physiological responses to light intensity derived from studies applying different photoperiods to different taxa, because different taxa show differential, even opposite growth responses to photoperiods and light intensities.

光驱动浮游植物的光合作用，因此，根据季节，纬度，深度和混合事件，其生活环境中的浮游植物必须利用可变的光照水平和暴露时间。比较生长，生理和生化组合物进行了探索的小Alexnadrium藻（〜40微米³ biovolume）和大链状亚历山大藻（~9300微米³ biovolume），全球广泛传播沿海有毒赤潮甲藻，响应于光周期的矩阵（光：黑暗，8：16、16：8和24：0）和生长光辐照度。在生长光水平较短的光周期下，较小的A. minutum生长更快，而较大的A. catenella在最低的光照条件下，较长的光周期下生长最快。光系统II功能在整个光周期长度上对瞬时生长光水平有很大的响应，而基于细胞生物量的呼吸，抗氧化能力以及细胞组成对光周期持续时间的响应比对光水平的响应更大。这些复杂的光生理反应分解为生长速率与细胞抗氧化剂活性和黑暗呼吸之间的线性相关性，表明呼吸使细胞抗氧化剂系统活跃起来，从而有益于细胞的生长。这些结果表明亚历山大的生长反应物种到整个光周期的光照水平随物种而变化，并且可能随细胞大小而变化。连同先前的结果，这对从对不同分类群应用不同光周期的研究得出的对光强度的生理反应的荟萃分析外推时要格外注意，因为不同的分类群对光周期和光强度显示出不同的甚至是相反的生长响应。