Table_1_Elevated pCO2 Impedes Succession of Phytoplankton Community From Diatoms to Dinoflagellates Along With Increased Abundance of Viruses and Bacteria.xlsx

Eutrophic coastal regions are highly productive and greatly influenced by human activities. Primary production supporting the coastal ecosystems is supposed to be affected by progressive ocean acidification driven by increasing CO2 emissions. In order to investigate the effects of high pCO2 (HC) on eutrophic plankton community structure and ecological functions, we employed 9 mesocosms and carried out an experiment under ambient (∼410 ppmv) and future high (1000 ppmv) atmospheric pCO2 conditions, using in situ plankton community in Wuyuan Bay, East China Sea. Our results showed that HC along with natural seawater temperature rise significantly boosted biomass of diatoms with decreased abundance of dinoflagellates in the late stage of the experiment, demonstrating that HC repressed the succession from diatoms to dinoflagellates, a phenomenon observed during algal blooms in the East China Sea. HC did not significantly influence the primary production or biogenic silica contents of the phytoplankton assemblages. However, the HC treatments increased the abundance of viruses and heterotrophic bacteria, reflecting a refueling of nutrients for phytoplankton growth from virus-mediated cell lysis and bacterial degradation of organic matters. Conclusively, our results suggest that increasing CO2 concentrations can modulate plankton structure including the succession of phytoplankton community and the abundance of viruses and bacteria in eutrophic coastal waters, which may lead to altered biogeochemical cycles of carbon and nutrients.

富营养化沿海区域具有极高的初级生产力，且深受人类活动影响。维系沿海生态系统的初级生产力，预计会受到二氧化碳排放增加驱动的渐进式海洋酸化的影响。为探究高二氧化碳分压（high pCO2，下文简称HC）对富营养化浮游生物群落结构与生态功能的影响，本研究设置9个中型围隔生态系统（mesocosms），以东海五缘湾的原位浮游生物群落为研究对象，在当前大气二氧化碳分压（约410 ppmv）及未来高分压（1000 ppmv）条件下开展实验。实验后期结果显示，HC与自然海水升温共同作用，显著提升了硅藻的生物量，同时降低了甲藻的丰度，表明HC抑制了硅藻向甲藻的群落演替——这一现象曾在东海赤潮过程中被观测到。HC并未显著影响浮游植物群落的初级生产力或生物源硅含量。但HC处理组提升了病毒与异养细菌的丰度，这反映出病毒介导的细胞裂解及细菌降解有机质过程，为浮游植物生长补充了营养盐。综上，本研究结果表明，二氧化碳浓度升高可调控富营养化沿海水域的浮游生物群落结构，包括浮游植物群落演替以及病毒与细菌的丰度，这可能会改变碳与营养盐的生物地球化学循环。