Direct linkage between dimethyl sulfide production and microzooplankton grazing, resulting from prey composition change under high partial pressure of carbon dioxide conditions@en

Oceanic dimethyl sulfide (DMS) is the enzymatic cleavage product of the algal metabolite dimethylsulfoniopropionate (DMSP) and is the most abundant form of sulfur released into the atmosphere. To investigate the effects of two emerging environmental threats (ocean acidification and warming) on marine DMS production, we performed a large-scale perturbation experiment in a coastal environment. At both ambient temperature and 2 °C warmer, an increase in partial pressure of carbon dioxide (pCO2) in seawater (160-830 ppmv pCO2) favored the growth of large diatoms, which outcompeted other phytoplankton species in a natural phytoplankton assemblage and reduced the growth rate of smaller, DMSP-rich phototrophic dinoflagellates. This decreased the grazing rate of heterotrophic dinoflagellates (ubiquitous micrograzers), resulting in reduced DMS production via grazing activity. Both the magnitude and sign of the effect of pCO2 on possible future oceanic DMS production were strongly linked to pCO2-induced alterations to the phytoplankton community and the cellular DMSP content of the dominant species and its association with micrograzers.海洋二甲基硫（DMS）是藻类代谢产物二甲基巯基丙酸内盐（DMSP）经酶解产生的产物，亦是释放至大气中的丰度最高的硫形态。为探究海洋酸化与增温这两种新兴环境威胁对海洋DMS生成过程的影响，我们在近岸生境中开展了大规模野外扰动实验。在环境温度与升温2℃的两组处理中，海水二氧化碳分压（pCO2）升高（范围为160~830ppmv pCO2）均促进了大型硅藻的生长：这类硅藻在自然浮游植物群落中通过竞争排挤其他浮游植物类群，并抑制了个体更小、富含DMSP的光合型甲藻的生长速率。这一变化降低了异养型甲藻（广布性微型浮游摄食者）的摄食速率，进而通过摄食活动介导的DMS生成途径减少了DMS的产生量。二氧化碳分压对未来海洋DMS生成的影响强度与方向，均与pCO2诱导的浮游植物群落结构改变、优势种的细胞内DMSP含量及其与微型浮游摄食者的互作密切相关。