Interacting effects of CO2 partial pressure and temperature on photosynthesis and calcification in a scleractinian coral, 2003

We show here that CO2 partial pressure (pCO2) and temperature significantly interact on coral physiology. The effects of increased pCO2 and temperature on photosynthesis, respiration and calcification rates were investigated in the scleractinian coral Stylophora pistillata. Cuttings were exposed to temperatures of 25°C or 28°C and to pCO2 values of ca. 460 or 760 muatm for 5 weeks. The contents of chlorophyll c2 and protein remained constant throughout the experiment, while the chlorophyll a content was significantly affected by temperature, and was higher under the 'high-temperature-high-pCO2' condition. The cell-specific density was higher at 'high pCO2' than at 'normal pCO2' (1.7 vs. 1.4). The net photosynthesis normalized per unit protein was affected by both temperature and pCO2, whereas respiration was not affected by the treatments. Calcification decreased by 50% when temperature and pCO2 were both elevated. Calcification under normal temperature did not change in response to an increased pCO2. This is not in agreement with numerous published papers that describe a negative relationship between marine calcification and CO2. The confounding effect of temperature has the potential to explain a large portion of the variability of the relationship between calcification and pCO2 reported in the literature, and warrants a re-evaluation of the projected decrease of marine calcification by the year 2100.

本研究证实，二氧化碳分压（CO2 partial pressure, pCO2）与温度对珊瑚生理过程存在显著交互作用。本研究以石珊瑚目珊瑚（scleractinian coral）指状多孔螅（Stylophora pistillata）为对象，探究了升高的pCO2与温度对其光合速率、呼吸速率及钙化速率的影响。将珊瑚断枝分别置于25℃或28℃温度、约460或760微大气压（microatmosphere, muatm）的pCO2环境中培养5周。

实验全程中，叶绿素c2（chlorophyll c2）与蛋白质含量均保持稳定；而叶绿素a（chlorophyll a）含量显著受温度影响，在“高温高pCO2”条件下含量更高。细胞特异性密度在高pCO2条件下高于正常pCO2条件（1.7 vs 1.4）。经单位蛋白质归一化后的净光合速率同时受温度与pCO2的影响，而呼吸速率则不受本实验处理的影响。当温度与pCO2均升高时，钙化速率下降了50%；而在常温条件下，钙化速率并未随pCO2升高而发生显著变化。

该结果与诸多已发表文献中报道的海洋钙化作用与CO2间的负相关关系不符。温度的混淆效应可解释文献中报道的钙化作用与pCO2间关系的大部分变异，因此有必要重新评估到2100年海洋钙化作用的预计下降幅度。