Seawater carbonate chemistry and particulate organic carbon accumulation of two Antarctic diatom species@en

Impacts of rising atmospheric CO2 concentrations and increased daily irradiances from enhanced surface water stratification on phytoplankton physiology in the coastal Southern Ocean remain still unclear. Therefore, in the two Antarctic diatoms Fragilariopsis curta and Odontella weissflogii the effects of moderate and high natural solar radiation combined with either ambient or future pCO2 on cellular particulate organic carbon (POC) contents and photophysiology were investigated. Results showed that increasing CO2 concentrations had greater impacts on diatom physiology than exposure to increasing solar radiation. Irrespective of the applied solar radiation regime, cellular POC quotas increased with future pCO2 in both diatoms. Lowered maximum quantum yields of photochemistry in PSII (Fv/Fm) indicated a higher photosensitivity under these conditions, being counteracted by increased cellular concentrations of functional photosynthetic reaction centers. Overall, our results suggest that both bloom‐forming Antarctic coastal diatoms might increase carbon contents under future pCO2 conditions despite reduced physiological fitness. This indicates a higher potential for primary productivity by the two diatom species with important implications for the CO2 sequestration potential of diatom communities in the future coastal Southern Ocean.南大洋沿岸海域中，大气二氧化碳浓度上升以及表层水体层化加剧导致的日辐射强度增加，二者对浮游植物生理的影响迄今仍未明确。鉴于此，本研究以两种南极硅藻——曲脆杆藻（Fragilariopsis curta）与威氏齿藻（Odontella weissflogii）为实验材料，探究了中等强度、高强度自然太阳辐射，分别结合当前环境二氧化碳分压与未来预期二氧化碳分压，对细胞颗粒有机碳（particulate organic carbon, POC）含量及光生理特性的影响。结果显示，相较于太阳辐射增强，二氧化碳浓度升高对硅藻生理的调控效应更为显著。无论施加何种太阳辐射处理模式，两种硅藻的细胞颗粒有机碳配额均随未来预期二氧化碳分压升高而提升。光系统II（PSII）的最大光化学量子产量（Fv/Fm）降低，表明该条件下光合敏感性增强，而功能性光合反应中心的细胞浓度升高可抵消这一效应。总体而言，本研究结果表明，尽管生理适配性有所下降，两种可形成水华的南极沿岸硅藻在未来二氧化碳分压环境下，其细胞碳含量或可提升。这意味着两种硅藻的初级生产潜力将有所提升，对未来南大洋沿岸硅藻群落的碳汇潜力具有重要意义。