Seawater carbonate chemistry and growth rate, cellular POC, PON, PIC contents

Coccolithophores are important oceanic primary producers not only in terms of photosynthesis but also because they produce calcite plates called coccoliths. Ongoing ocean acidification associated with changing seawater carbonate chemistry may impair calcification and other metabolic functions in coccolithophores. While short‐term ocean acidification effects on calcification and other properties have been examined in a variety of coccolithophore species, long‐term adaptive responses have scarcely been documented, other than for the single species Emiliania huxleyi . Here, we investigated the effects of ocean acidification on another ecologically important coccolithophore species, Gephyrocapsa oceanica, following 1,000 generations of growth under elevated CO2 conditions (1,000 μatm). High CO2‐selected populations exhibited reduced growth rates and enhanced particulate organic carbon (POC ) and nitrogen (PON ) production, relative to populations selected under ambient CO2 (400 μatm). Particulate inorganic carbon (PIC ) and PIC /POC ratios decreased progressively throughout the selection period in high CO2‐selected cell lines. All of these trait changes persisted when high CO2‐grown populations were moved back to ambient CO2 conditions for about 10 generations. The results suggest that the calcification of some coccolithophores may be more heavily impaired by ocean acidification than previously predicted based on short‐term studies, with potentially large implications for the ocean's carbon cycle under accelerating anthropogenic influences.

颗石藻（Coccolithophores）是重要的海洋初级生产者，其重要性不仅体现在光合作用层面，更在于它们能够合成名为颗石粒（coccoliths）的钙质鳞片。当前伴随海水碳酸盐化学变化的海洋酸化（ocean acidification），可能会损害颗石藻的钙化作用及其他代谢功能。尽管学界已针对多种颗石藻物种开展了短期海洋酸化对钙化及其他性状的影响研究，但除赫氏颗石藻（Emiliania huxleyi）这一单一物种外，长期适应性响应的相关记录仍极为匮乏。本研究以另一生态重要性显著的颗石藻物种——大洋桥石藻（Gephyrocapsa oceanica）为对象，探究了其在高CO₂（1000 μatm）条件下连续培养1000代后，海洋酸化所产生的影响。相较于在环境CO₂（400 μatm）条件下选育的种群，高CO₂选育种群的生长速率有所降低，而颗粒有机碳（POC）与颗粒氮（PON）的合成量则显著提升。在整个选育周期中，高CO₂选育细胞系的颗粒无机碳（PIC）以及PIC/POC比值均呈持续下降趋势。当将高CO₂培养的种群转移至环境CO₂条件下培养约10代后，上述所有性状变化仍持续存在。本研究结果显示，部分颗石藻的钙化作用受海洋酸化的损害程度或远超此前基于短期研究的预测，这在人为活动影响加剧的背景下，可能对海洋碳循环产生重大潜在影响。