模拟大气 CO2水平升高对春季太湖浮游植物生理特性的影响

基于2012年春季在太湖梅梁湾进行为期27 d的不同CO2水平(大气CO2体积分数(CO2,g])梯度为270×10-6、380×10-6、750×10-6)的野外培养实验,揭示了大气CO2水平升高对太湖浮游植物的碳源选择、生长速率、光合作用、净初级生产力和细胞化学元素组成等生理过程的影响,结果表明,大气CO2浓度的升高首先会显著改变太湖水体的pH值和碳化学环境,减弱浮游植物碳浓缩机制(CCM)的必要性.大气CO2浓度加倍后,浮游植物的最大生长速率(Umax)、净初级生产力(NPP)、单位叶绿素a(Chl-a)含量的NPP会分别增加63.1%、69.6%、33.8%.大气CO2浓度的升高会促进太湖绿藻和硅藻的最大光合作用效率并且其对硅藻的促进作用比绿藻更显著,但并没有改变春季蓝藻光合作用活性极低的现状.大气CO2浓度的升高在提高浮游植物细胞中C、N含量的同时,却减少了P的吸收.本研究结果将为预测和揭示太湖浮游植物对未来气候变化的响应提供理论基础.

Effects of Simulated Elevation of Atmospheric CO2 Concentration on the Physiological Features of Spring Phytoplankton in Taihu Lake

To disclose the impact of different CO₂ concentrations (270×10^-6, 380×10^-6, 750×10^-6) on physiological features of spring phytoplankton, an in situ simulated experiment was carried out in Meiliang Bay of Taihu Lake from 29 April to 26 May in 2012. The results showed that atmospheric CO₂ elevation would significantly alter the pH value and carbonate chemical environments of Taihu Lake, resulting in weakening the advantages of carbon concentrating mechanism (CCM) of phytoplankton. Phytoplankton in Taihu Lake tended to use more dissolved CO₂(CO_{2, aq}) due to the deliberate CO₂ sequestration under the high CO₂ level treatment. When atmospheric CO₂ concentration doubles at the end of century, the maximum growth rate constant of phytoplankton (U_max), NPP, chlorophyll a (Chl-a)-specific NPP would increase by 63.1%, 69.6% and 33.8%,respectively. Atmospheric CO₂ elevation promoted the maximum photosynthetic efficiency of chlorophyta and bacillariophyta in Taihu Lake and its promotion effect on bacillariophyta was more notable than that on chlorophyta. However, it did not change the photosynthetic efficiency of cyanobacteria which was very low in spring. Meanwhile, the stoichiometry value of phytoplankton changed significantly due to the CO₂ elevation, as phytoplankton cells assimilated more C and N, but less P under the treatment of high CO₂ level. Our results indicated the enhanced CO₂ level could dramatically change the physiological features of phytoplankton, This information would help us to understand and predict the response of phytoplankton in Taihu Lake to the future climate change.