Interactive effects of warming and ocean acidification on the Arctic picoeukaryote Micromonas pusilla

In the Arctic Ocean, climate change effects such as warming and ocean acidification (OA) are manifesting faster than in other regions. Yet, we are lacking a mechanistic understanding of the interactive effects of these drivers on Arctic primary producers. In the current study, one of the most abundant species of the Arctic Ocean, the prasinophyte Micromonas pusilla, was exposed to a range of different pCO2levels at two temperatures representing realistic scenarios for current and future conditions. We observed that warming and OA synergistically increased growth rates at intermediate to high pCO2 levels. Furthermore, elevated temperatures shifted the pCO2-optimum of biomass production to higher levels. Based on changes in cellular composition and photophysiology, we hypothesise that the observed synergies can be explained by beneficial effects of warming on carbon fixation in combination with facilitated carbon acquisition under OA. Our findings help to understand the higher abundances of picoeukaryotes such as M. pusilla under OA, as has been observed in many mesocosm studies.

北冰洋相较于全球其他海域，气候变暖与海洋酸化（Ocean Acidification, OA）等气候变化影响的显现进程更为迅速。
然而，目前学界对这两类环境驱动因子对北冰洋初级生产者的交互效应仍缺乏机制层面的深入认知。
本研究以北冰洋最为丰富的物种之一——平藻纲微小微单胞藻（Micromonas pusilla）为研究对象，设置了一系列不同二氧化碳分压（partial pressure of CO₂, pCO₂）梯度，并采用代表当前及未来真实气候情景的两个温度条件开展培养实验。
实验结果显示，在中等至高二氧化碳分压条件下，变暖和海洋酸化可协同提升该藻的生长速率。此外，升温处理将该藻生物量生产的二氧化碳分压最优值向更高区间偏移。
基于细胞组成与光生理特性的变化，本研究提出假说：观测到的协同效应可归因于升温对碳固定的有益作用，与海洋酸化环境下碳摄取过程的强化共同作用的结果。
本研究结果有助于解释为何在海洋酸化环境下，微小微单胞藻这类微微型真核浮游生物（picoeukaryotes）的丰度会升高——这一现象已在多项原位围隔实验（mesocosm studies）中被观测到。