高浓度CO2引起的海水酸化对小珊瑚藻光合作用和钙化作用的影响

为了探讨CO2海底封存潜在的渗漏危险对于海洋生物的可能影响,以大型钙化藻类小珊瑚藻(Corallina pilulifera)为研究对象,在室内控光控温条件下,通过向培养海水充入CO2气体得到3种不同酸化程度的培养条件(pH 8.1、6.8和5.5),24h后比较藻体光合作用和钙化作用情况。结果显示:相对于自然海水培养条件(pH 8.1),在pH 6.8条件下培养的小珊瑚藻光合固碳速率得到了增强,而在pH 5.5条件下光合固碳速率则降低;随着酸化程度的增强,藻体的钙化固碳速率越来越低,在pH 5.5条件下甚至表现为负值(-2.53±0.57)mg C g-1干重h-1];藻体颗粒无机碳(PIC)和颗粒有机碳(POC)含量的比值随着酸化程度的加强而降低,这反映了酸化对光合和钙化作用的综合效应。快速光反应曲线的测定结果显示:随着酸化程度的增强,强光引起的光抑制程度越来越强;在酸化条件下,藻体的光饱和点显著降低,但pH 6.8和5.5之间没有显著差异;低光下的电子传递速率在pH 8.1和6.8之间没有显著差异,pH 5.5培养条件下显著降低;最大电子传递速率在pH 6.8时最大,在pH 5.5时最低。以上结果说明,高浓度CO2引起的海水酸化显著地影响着小珊瑚藻的光合和钙化过程,不同的酸化程度下,藻体的光合、钙化反应不同,在较强的酸化程度下(pH 5.5),藻体的光合和钙化过程都将受到强烈的抑制,这些结果为认识CO2海底封存渗漏危险对海洋钙化藻类的可能影响提供了理论参考。

Effects of CO2-induced seawater acidification on photosynthesis and calcification in the coralline alga Corallina pilulifera

Increasing atmospheric CO2 is causing global public concern and seabed sequestration is one possible method of carbon reduction.However,studies on the potential risk of CO2 leakage and its possible effects on the marine environment are still very limited.To investigate such possible effects on sensitive marine organisms,coralline algae,Corallina pilulifera,were cultured under controlled conditions: 20℃,100μmol photons m-2 s-1 and a light period of 12h.Three treatments were set at acidities of pH 8.1,6.8 and 5.5,by aerating natural seawater with pure gaseous CO2.After 24 hours,photosynthesis and calcification rates of C.pilulifera cultured at different pH levels were determined.The rate of photosynthetic carbon fixation was enhanced at the pH of 6.8 and was inhibited at the pH of 5.5,compared with the algae grown in the seawater control(pH 8.1).The rate of calcified carbon fixation was depressed with decreasing pH,and even exhibited a negative value (-2.53±0.57) mg C(g DW)-1 h-1] at pH 5.5.Additionally,with the decrease in pH,the ratio of particulate inorganic carbon(PIC) to particulate organic carbon(POC) content in the algae,measured with a vario TOC cube,decreased remarkably,which reflected the comprehensive effects of CO2-induced seawater acidification on photosynthesis and calcification.Rapid light curves of algae cultured at different pH levels,which indicated the responses of electron transport rates(ETR) in photosystem II(PS II) to irradiance,were determined by pulse amplitude modulated chlorophyll fluorescence(PAM).The results showed that the photoinhibition term(a) increased with the decrease in pH,indicating that algae grown at lower pH levels experience greater photoinhibition.The light saturation point(Ik) decreased significantly under the CO2-induced acidification conditions,though a significant difference was not found between pH of 6.8 and 5.5.The initial slope of the rapid light curve(α),reflecting the efficiency of the electron transport rate at low irradiance,was lower at pH 5.5 than at the other two levels,while there was no significant difference between pH 8.1 and 6.8 levels.The maximum relative electron transport rate(rETRmax) exhibited the highest value in algae cultured at pH 6.8 and the lowest at pH 5.5.According to these results,we concluded that CO2-induced seawater acidification noticeably affected the photosynthesis and calcification of C.pilulifera,and different degrees of acidification caused different responses of photosynthesis and calcification.At the lowest pH level(pH 5.5),both the photosynthesis and calcification of C.pilulifera were significantly inhibited.These results provide a reference for studies on the risk of CO2 leakage from seabed sequestration methods on the physiology and ecology of marine coralline algae.