Seawater carbonate chemistry and Emiliania huxleyi biological processes during experiments, 2010@en

The calcifying phytoplankton species, coccolithophores, have their calcified coccoliths around the cells, however, their physiological roles are still unknown. Here, we hypothesized that the coccoliths may play a certain role in reducing solar UV radiation (UVR, 280-400 nm) and protect the cells from being harmed. Cells of Emiliania huxleyi with different thicknesses of the coccoliths were obtained by culturing them at different levels of dissolved inorganic carbon and their photophysiological responses to UVR were investigated. Although increased dissolved inorganic carbon decreased the specific growth rate, the increased coccolith thickness significantly ameliorated the photoinhibition of PSII photochemical efficiency caused by UVR. Increase by 91% in the coccolith thickness led to 35% increase of the PSII yield and 22% decrease of the photoinhibition of the effective quantum yield by UVR. The coccolith cover reduced more UVA (320-400 nm) than UVB (280-315 nm), leading to less inhibition per energy at the UV-A band.

钙化浮游植物类群颗石藻（coccolithophores）的细胞表面覆盖有钙化颗石片，但其生理功能至今仍未明确。本研究提出假说：颗石片或可在削弱太阳紫外线辐射（UVR，280-400 nm）的过程中发挥一定作用，从而保护细胞免受辐射损伤。研究通过调控培养体系中溶解无机碳的浓度，获得了颗石片厚度各异的赫氏颗石藻（Emiliania huxleyi）细胞，并对其在UVR胁迫下的光生理响应展开了探究。尽管溶解无机碳浓度升高会降低藻细胞的比生长速率，但颗石片厚度的增加可显著缓解UVR诱导的光系统II（PSII）光化学效率光抑制。当颗石片厚度提升91%时，PSII量子产额可增加35%，而UVR导致的有效量子产额光抑制程度降低22%。相较于紫外线B（UVB，280-315 nm），颗石片覆盖层对紫外线A（UVA，320-400 nm）的屏蔽效果更为显著，使得UV-A波段单位能量对应的辐射抑制效应更弱。