Copepod grazing and prokaryotic decomposition amplify the effect of diatom/dinoflagellate regime change on biological carbon pump efficiency

The Biological Carbon Pump (BCP) plays a critical role in global carbon sequestration by exporting particulate organic carbon (POC) from surface waters to the ocean's depths. Copepod fecal pellets (FPs) are an important but highly variable component of the global BCP. This study decoupled and quantified how copepod grazing and prokaryotic activities affect BCP efficiency under different phytoplankton dietary regimes. Controlled experiments revealed that, with a diet of diatoms, copepods double FP production rates, triple FP sinking rates, and significantly lower FP decomposition rates relative to those withe dinoflagellate diets. These biological activities synergistically enhance the efficiency of diatom FP exports to the deep ocean. Opportunistic particle-attached (PA) prokaryotes were crucial to FP decomposition. Metagenomic analyses revealed that functional enzymes targeting phytoplankton- and copepod intestine-derived macromolecules from the PA prokaryotic communities were key to FP decomposition. Genomic properties of Planctomycetota revealed that the strong motile ability, detoxification systems and macromolecule degradation enzymes enabled the success of these opportunistic prokaryotes. Elevated temperatures amplified decomposition rates by enhancing enzyme activities, thus reducing BCP efficiency as recycled organic material would remain in surface waters. Our findings highlight the synergistic biological activities amplifying the effects of phytoplankton composition changes on BCP efficiency. This underscores the importance of considering grazing regimes in combination with microbial dynamics in assessing oceanic carbon cycling.

生物碳泵（Biological Carbon Pump, BCP）通过将颗粒有机碳（particulate organic carbon, POC）从表层海水输送至海洋深处，在全球碳封存过程中发挥关键作用。桡足类粪粒（copepod fecal pellets, FPs）是全球生物碳泵中一类重要但高度可变的组成部分。本研究解耦并量化了不同浮游植物食性条件下，桡足类牧食活动与原核生物活动对生物碳泵效率的影响。
受控实验结果显示，相较于甲藻食性，以硅藻为食的桡足类粪粒生产速率提升一倍，沉降速率提升三倍，且粪粒分解速率显著降低。上述生物活动协同增强了硅藻源粪粒向深海输送的效率。
附粒（particle-attached, PA）原核生物是粪粒分解的关键类群。宏基因组分析表明，附粒原核生物群落中靶向浮游植物及桡足类肠道来源大分子的功能酶，是粪粒分解的核心驱动因素。浮霉菌门（Planctomycetota）的基因组特征显示，其较强的运动能力、解毒系统及大分子降解酶类，助力这类机会性原核生物获得生存优势。
温度升高通过增强酶活性提升了粪粒分解速率，使得循环利用的有机物质留存于表层海水，进而降低了生物碳泵效率。本研究结果凸显了协同生物活动可放大浮游植物组成变化对生物碳泵效率的影响，强调了在评估海洋碳循环时，需综合考量牧食模式与微生物动态的重要性。