Seawater carbonate chemistry, pigments and biological processes during experiments with coralline alga Corallina sessilis

Previous studies have shown that increasing atmospheric CO2 concentrations affect calcification in some planktonic and macroalgal calcifiers due to the changed carbonate chemistry of seawater. However, little is known regarding how calcifying algae respond to solar UV radiation (UVR, UVA+UVB, 280-400 nm). UVR may act synergistically, antagonistically or independently with ocean acidification (high CO2/low pH of seawater) to affect their calcification processes. We cultured the articulated coralline alga Corallina sessilis Yendo at 380 ppmv (low) and 1000 ppmv (high) CO2 levels while exposing the alga to solar radiation treatments with or without UVR. The presence of UVR inhibited the growth, photosynthetic O2evolution and calcification rates by13%, 6% and 3% in the low and by 47%, 20% and 8% in the high CO2 concentrations, respectively, reflecting a synergistic effect of CO2 enrichment with UVR. UVR induced significant decline of pH in the CO2-enriched cultures. The contents of key photosynthetic pigments, chlorophyll a and phycobiliproteins decreased, while UV-absorptivity increased under the highpCO2/low pH condition. Nevertheless, UV-induced inhibition of photosynthesis increased when the ratio of particulate inorganic carbon/particulate organic carbon decreased under the influence of CO2-acidified seawater, suggesting that the calcified layer played a UV-protective role. Both UVA and UVB negatively impacted photosynthesis and calcification, but the inhibition caused by UVB was about 2.5-2.6 times that caused by UVA. The results imply that coralline algae suffer from more damage caused by UVB as they calcify less and less with progressing ocean acidification.

已有研究表明，大气CO₂浓度升高会通过改变海水的碳酸盐化学性质（carbonate chemistry），影响某些浮游和大型藻类钙化生物（planktonic and macroalgal calcifiers）的钙化作用（calcification）。然而，关于钙化藻类（calcifying algae）如何响应太阳紫外线辐射（UVR，UVA+UVB，280-400 nm）的研究尚少。UVR可能与海洋酸化（海水高CO₂/低pH，Ocean Acidification）产生协同、拮抗或独立作用，从而影响其钙化过程。我们将节肢红藻Corallina sessilis Yendo培养在380 ppmv（低）和1000 ppmv（高）的CO₂水平下，同时对其进行有无UVR的太阳辐射处理。在低CO₂浓度下，UVR的存在分别抑制了其生长、光合放氧（photosynthetic O₂ evolution）和钙化速率13%、6%和3%；在高CO₂浓度下，上述抑制率分别为47%、20%和8%，这反映了CO₂富集（CO₂ enrichment）与UVR的协同效应。UVR导致富CO₂培养体系（CO₂-enriched cultures）中的pH显著下降。在高pCO₂/低pH条件（high pCO₂/low pH condition）下，关键光合色素（photosynthetic pigments）（叶绿素a和藻胆蛋白）的含量降低，而紫外线吸收能力（UV-absorptivity）增强。然而，在CO₂酸化海水（CO₂-acidified seawater）的影响下，当颗粒无机碳（particulate inorganic carbon）与颗粒有机碳（particulate organic carbon）的比值降低时，UV诱导的光合作用（photosynthesis）抑制作用增强，这表明钙化层（calcified layer）具有紫外线保护作用（UV-protective role）。UVA和UVB均对光合作用和钙化产生负面影响，但UVB造成的抑制作用约为UVA的2.5-2.6倍。研究结果表明，随着海洋酸化的加剧，珊瑚藻（coralline algae）的钙化作用逐渐减弱，其受到UVB的伤害也会随之增加。