Phytoplankton in the upper oceans are exposed to changing light levels due to mixing, diurnal solar cycles and weather conditions. Consequently, effects of ocean acidification are superimposed upon responses to variable light levels. We therefore grew a model diatom Thalassiosira pseudonana under either constant or variable light but at the same daily photon dose, with current low (400 μatm, LC) and future high CO2 (1000 μatm, HC) treatments. Variable light, compared with the constant light regime, decreased the growth rate, Chl a, Chl c, and carotenoid contents under both LC and HC conditions. Cells grown under variable light appeared more tolerant of high light as indicated by higher maximum relative electron transport rate and saturation light. Light variation interacted with high CO2/lowered pH to decrease the carbon fixation rate, but increased particulate organic carbon (POC) and particularly nitrogen (PON) per cell, which drove a decrease in C/N ratio, reflecting changes in the efficiency of energy transfer from photo-chemistry to net biomass production. Our results imply that elevated pCO2 under varying light conditions can lead to less primary productivity but more PON per biomass of the diatom, which might improve the food quality of diatoms and thereby influence biogeochemical nitrogen cycles.

中文翻译：

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海洋酸化作用与可变光相互作用，从而减少了硅藻的生长，但增加了硅藻中有机氮的产生。

由于混合，日照周期和天气条件的影响，上层海洋中的浮游植物暴露于变化的光照水平。因此，海洋酸化的影响会叠加在对可变光照水平的响应上。因此，我们在恒定或可变光下，但在相同的每日光子剂量下，用当前的低（400μatm，LC）和未来的高CO2（1000μatm，HC）处理方法生长了一个模型硅藻Thalassiosira pseudonana。与恒定光照相比，可变光照降低了LC和HC条件下的生长速率，Chl a，Clc和类胡萝卜素含量。在较高的最大相对电子传输速率和饱和光的指示下，在可变光下生长的细胞表现出对高光的耐受性。光照变化与高CO2 /降低pH相互作用，降低了固碳率，但是每个电池中颗粒有机碳（POC）的增加，尤其是氮（PON）的增加，导致C / N比降低，反映了从光化学到净生物质生产的能量转移效率的变化。我们的结果表明，在变化的光照条件下升高的pCO2会导致初级生产力降低，但硅藻的每个生物量的PON增多，这可能会改善硅藻的食品质量，从而影响生物地球化学氮循环。