绿潮藻浒苔光合固碳与防治海水酸化的作用Ⅰ.光合固碳与海水pH值提高速率研究

以黄海绿潮暴发的主要漂浮种类浒苔 (Ulva prolifera)为材料,在实验室条件下研究了浒苔光合参数、固碳速率及提升海水pH的作用,结果表明:浒苔光合作用半饱和常数K_m为0.25 mmol/dm3,光合作用饱和时海水溶解无机碳(DIC)浓度也只需1.2 mmol/dm3,为正常海水DIC浓度(2.4 mmol/dm3)一半,故黄海绿潮暴发时藻体可以一直保持光合作用饱和与旺盛生长状态。水生条件下浒苔藻体主要吸收海水中的DIC,0.5 g/dm3培养密度下,1个光周期内净光合固碳速率为10.92 mg /(g·d)(鲜重)。连续培养5 d,0.5,1.0和2.5 g/dm3培养密度组的DIC浓度从22 mg/dm3分别降为4.85,2.62和0.66 mg/dm3,表明DIC去除率随藻体培养密度提高而增强,分别可达77.78%,88.00%,96.98%;藻体吸收海水中无机碳的同时可使海水pH升高,0.5 g/dm3培养密度下,1个光周期内净提升pH速率高达0.96/(dm3·g·d)。连续培养5 d,0.5,1.0和2.5 g/dm3培养密度组第1天其pH分别可达到9.1,9.2和9.7,表明藻体密度越高pH提升越快,而且第5天pH均可稳定在9.9左右。浒苔暴露在空气中可直接吸收空气中CO₂,1个光周期内其光合固碳速率约为46.14 mg/(g·d),而在海水中的光合固碳速率为10.92 mg/(g·d),可见浒苔在空气中的光合固碳速率是水中的4.23倍。水生和气生时单位质量藻体的固碳效率因藻体间相互遮蔽而下降。结果可为今后黄海绿潮暴发机制及CO₂减排和防止海洋酸化作用的评估提供技术支撑。

Studies on photosynthesis carbon fixation and ocean acidification prevention in Ulva prolifera I.Rate of photosynthesis carbon fixation and seawater pH increase

The effects of DIC levels on the photosynthesis of Ulva prolifera, carbon absorbing capacity at aquatic and aerial state, and pH value improving ability, were studied under laboratory conditions. The results show that the value of K_m (DIC) for photosynthesis of U. prolifera is 0.25 mmol/dm³, and photosynthesis of U. prolifera is saturated at 1.2mmol/dm³ of DIC concentration in seawater, which is extremely lower than ambient DIC concentration(2.4 mmol/dm³, DIC) in normal seawater. It indicates that the blades in U. prolifera could keep a vigorous photosynthesis and growth during "green tide" blooming. In seawater, the blades of U. prolifera absorbed the DIC from seawater. Cultured with blade density of 0.5 g/dm³, the rate of carbon fixation of U. prolifera by photosynthesis is 10.92 mg/(g·d)(FW) for one photosynthesis period. Cultured for 5 d, the DIC concentration in 0.5, 1.0 and 2.5 g/dm³ blade density groups decreases to 4.85, 2.62 and 0.66 mg/dm³ respectively. It indicates that DIC uptaking rate increases with the blade density increase, and the DIC concentration removal rate is 77.78%, 88.00% and 96.98% for 0.5, 1.0 and 2.5 g/dm³blade density groups, respectively. When blades absorbed the DIC out of seawater, they immediately increased the pH in seawater, and the rate for pH increasing reached to 0.96 /(dm³·g·d) in culture system with 0.5 g/dm³ blade density during one photosynthesis period. Cultured for 5 d, the pH value in 0.5, 1.0 and 2.5 g/dm³blade density groups increases to 9.1, 9.2 and 9.7 in the first culture day respectively, and keeps at 9.9 in the 5th day. It indicates that the higher the blade density, the higher the pH in culture system.When exposed in air, the blades could absorb the CO₂ from air. The rate of photosynthetic carbon fixation of U.prolifera in the air is about 46.14 mg/(g·d) during one photosynthesis period, and it is 4.23 times more than that in water. The photosynthesis carbon fixation efficiency for unit mass would decrease for shading among blades. It indicates that this study will provide the supports for green tide blooming mechanism study and estimating its CO₂ emission reduction and ocean acidification prevention.