作 者 ：张曼,曾波*,张怡,韩博平
期 刊 ：生态学报 2010年 30卷 24期 页码：7087~7091
Keywords:algae, electron transport rate, temperature, oxygen production,
摘 要 ：由于直接测定藻类的光合速率耗时且不方便，研究者们常通过测定藻类光合电子传递速率的方式来间接反映其光合速率，理论上，以氧气产生来度量的总光合速率（PGross）与电子传递速率(ETR)之间应该存在很好的线性关系。然而，由于温度的变化会影响藻类的光呼吸等耗氧的生理过程从而影响光合作用中的氧气释放，因此温度可能会对PGross与ETR之间的线性关系产生影响。研究了温度变化对蛋白核小球藻（Cholorella pyrenoidosa）、菱形藻（Nitzschia sp.）和水生集胞藻（Synechocystis aquetilis Sauv.）的总光合放氧速率（PGross）与电子传递速率(ETR)之间比率的影响，结果表明PGross/ETR随温度的升高而降低，低温条件下PGross/ETR比值较高，说明在相同的电子传递速率的情况下水的光裂解产生的氧有更多的可以释放出来；在高温条件下PGross/ETR比值相对较低，说明高温条件下可能有相对更多的水光裂解产生的氧被用于耗氧的生理过程而没有释放出来。研究表明当温度发生变化时，光合放氧与电子传递之间并不呈线性关系，这说明将ETR作为实际光合生产的评价指标时要谨慎，不能不加分析地直接应用。
Abstract:In algal research, oxygen evolution is often used as a direct measure of photosynthetic rate. Due to the facility and time limitation, however, direct measurement of oxygen evolution by algae sometimes is impracticable and inconvenient, and researchers therefore are often inclined to take electron transport rate (ETR) as an indirect measure of photosynthetic rate. Theoretically, in photosynthesis, the oxidization of two molecules of H2O leads to the production of one molecule of oxygen and four electrons; the electrons are ultimately transported to NADP+ and used to form NADPH, and oxygen is released to the atmosphere. In theory, there exists a linear relation of 0.25 molar ratio between oxygen evolution and electron transport. In algae, oxygen is involved as electron acceptor in many physiological processes such as chloro-respiration, water-water cycle, and photorespiration, which consequently affects the ultimate oxygen evolution in photosynthesis. Therefore, some researches have been conducted to ascertain whether oxygen evolution is linearly related with electron transport. It was found that if irradiance was saturated or dissolved inorganic carbon concentrations was changed, oxygen evolution did not present a linear relation with electron transport. However, under the condition of constant temperature, it was found that oxygen evolution was linearly related to electron transport. Because temperature affects many physiological processes in which oxygen is consumed (such as photorespiration), it is likely that oxygen evolution is not linearly related to electron transport as temperature changes. To test this hypothesis, three algal species, Chorella pyrenoidosa, Nitzschia sp. and Synechocystis aquetilis, belonging to chlorophyta, bacillariophyta, and cyanophyta, respectively, were selected in the experiment. Their electron transport rate and oxygen evolution under variable temperature conditions (10，15，20，25℃) were investigated, and the ratio of PGrosshotosynthesis (PGross, in terms of oxygen evolution) to electron transport rate was analyzed. The results showed that, for all three species, the ratio of PGross/ETR decreased significantly as temperature increased. At low temperature, the ratio of PGross/ETR was higher, which implies that more energy via electron transport might be used for photosynthesis and more oxygen was produced. On the contrary, at high temperature, the ratio of PGross/ETR was lower, which implies that presumably less energy via ETR was used to drive carbon fixation and oxygen evolution was reduced due to probable oxygen utilization in processes such as photorespiration. It is clear in this experiment that the relation between oxygen evolution rate and ETR was not linear, and was strikingly affected by temperature. Based on the experimental results, it is suggested that ETR measurements cannot be used to reliably estimate photosynthetic production under variable temperatures.
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