海水酸化和碱化对斑点海链藻光合生理特性的影响

大气CO₂浓度升高引起的海洋酸化可能对浮游植物造成不同程度的影响。而近海浮游植物不仅面临着海水酸化问题，还会受到海水溶解性CO₂降低及pH升高(海水碱化)的影响。本实验以斑点海链藻(Thalassiosira punctigera)为研究对象，测定7个不同pCO₂水平(25 μatm、50 μatm、100 μatm、200 μatm、400 μatm、800 μatm、1 600 μatm)下的生长、光合作用和呼吸作用速率、细胞粒径、叶绿素a和生物硅含量以及叶绿素荧光等参数。结果表明，与400 μatm相比，在海水酸化(pCO₂ > 400 μatm)和海水碱化(pCO₂ < 400 μatm) 条件下，斑点海链藻的生长速率和叶绿素a含量都显著降低，但是碱化条件下降低的程度更大。此外，碱化处理的藻细胞光合作用速率、最大量子产量(Fv/Fm)和最大相对电子传递速率(rETR_max)都显著低于400 μatm培养下的细胞，而呼吸作用速率显著升高，但是生物硅含量和细胞大小无明显变化。研究表明海水碱化和海水酸化均会抑制其生理活动，而且海水碱化对其影响更显著。这表明正常pCO₂生长下的藻细胞具有最适的生理状态。本研究可为探究海水碳酸盐系统变化对海洋初级生产力的影响提供一定的数据支持。

Effect of seawater acidification and alkalization on photosynthetic physiology of Thalassiosira punctigera

Increasing atmospheric CO₂ concentration leads to ocean acidification, which might affect phytoplankton to varying degrees. Phytoplankton in coastal waters may be affected by seawater acidification and alkalization. In this experiment, Thalassoosira punctigera (diatom) was used to investigate its growth, photosynthesis, dark respiration, cell size, chlorophyll a content, biogenic silica content and chlorophyll fluorescence at seven pCO₂ levels (25 μatm, 50 μatm, 100 μatm, 200 μatm, 400 μatm, 800 μatm, 1 600 μatm). The results showed that, compared with 400 μatm, the growth rate and chlorophyll a content in seawater acidification (pCO₂ > 400 μatm) and alkalization (pCO₂ < 400 μatm) treatments were significantly reduced, but the degree of decrease was greater under the condition of alkalization. In addition, cells showed lower photosynthesis rates and maximum quantum yield of PSII (Fv/Fm) and relative maximum electron transport rate (rETRmax) under alkalization conditions. However, there was no significant changes in biogenic silica content and cell size among different pCO₂ levels. We found both seawater alkalization and acidification could inhibit the physiological activities of T. punctigera, and seawater alkalization had much more inhibited effects. Our results showed that the cell grown at current pCO₂ level (400 μatm) had the optical physiological performance. Moreover, among the pCO₂ levels set in this study, seawater alkalization has a more significant effect on T. punctigera. The present study provides a theoretical basis for studying the effects of changing seawater carbonate chemistry on the marine primary productivity in coastal waters.