Goldman Johanna A L, Bender Michael L, Morel François M M
Department of Geosciences, Princeton University, Princeton, NJ, 08544, USA.
Center for Environmental Genomics, School of Oceanography, University of Washington, Seattle, WA, 98105, USA.
Photosynth Res. 2017 Apr;132(1):83-93. doi: 10.1007/s11120-016-0330-2. Epub 2017 Jan 6.
The response of marine phytoplankton to the ongoing increase in atmospheric pCO reflects the consequences of both increased CO concentration and decreased pH in surface seawater. In the model diatom Thalassiosira weissflogii, we explored the effects of varying pCO and pH, independently and in concert, on photosynthesis and respiration by incubating samples in water enriched in HO. In long-term experiments (6-h) at saturating light intensity, we observed no effects of pH or pCO on growth rate, photosynthesis or respiration. This absence of a measurable response reflects the very small change in energy used by the carbon concentrating mechanism (CCM) compared to the energy used in carbon fixation. In short-term experiments (3 min), we also observed no effects of pCO or pH, even under limiting light intensity. We surmise that in T. weissflogii, it is the photosynthetic production of NADPH and ATP, rather than the CO-saturation of Rubisco that controls the rate of photosynthesis at low irradiance. In short-term experiments, we observed a slightly higher respiration rate at low pH at the onset of the dark period, possibly reflecting the energy used for exporting H and maintaining pH homeostasis. Based on what is known of the biochemistry of marine phytoplankton, our results are likely generalizable to other diatoms and a number of other eukaryotic species. The direct effects of ocean acidification on growth, photosynthesis and respiration in these organisms should be small over the range of atmospheric pCO predicted for the twenty-first century.
海洋浮游植物对大气中pCO持续增加的响应反映了表层海水中CO浓度升高和pH值降低的双重后果。在模式硅藻威氏海链藻（Thalassiosira weissflogii）中，我们通过将样本置于富含HO的水中孵育，分别及共同探究了不同pCO和pH对光合作用和呼吸作用的影响。在饱和光照强度下进行的长期实验（约6小时）中，我们未观察到pH或pCO对生长速率、光合作用或呼吸作用有影响。这种未观察到可测量响应的情况反映出，与碳固定过程中所使用的能量相比，碳浓缩机制（CCM）所使用的能量变化非常小。在短期实验（约3分钟）中，即使在低光照强度下，我们也未观察到pCO或pH的影响。我们推测，在威氏海链藻中，是NADPH和ATP的光合产生，而非核酮糖-1,5-二磷酸羧化酶（Rubisco）的CO饱和状态，在低辐照度下控制着光合作用的速率。在短期实验中，我们观察到在黑暗期开始时，低pH条件下的呼吸速率略高，这可能反映了用于输出H和维持pH稳态所消耗的能量。基于对海洋浮游植物生物化学的了解，我们的结果可能适用于其他硅藻和许多其他真核生物物种。在预测的21世纪大气pCO范围内，海洋酸化对这些生物生长、光合作用和呼吸作用的直接影响应该很小。
