Seawater carbonate chemistry and growth rate during experiments with phylotypes of Symbiodinium (Dinophyceae), 2011

We investigated the effect of elevated partial pressure of CO2 (pCO2) on the photosynthesis and growth of four phylotypes (ITS2 types A1, A13, A2, and B1) from the genus Symbiodinium, a diverse dinoflagellate group that is important, both free-living and in symbiosis, for the viability of cnidarians and is thus a potentially important model dinoflagellate group. The response of Symbiodinium to an elevated pCO2 was phylotype-specific. Phylotypes A1 and B1 were largely unaffected by a doubling in pCO2 in contrast, the growth rate of A13 and the photosynthetic capacity of A2 both increased by ~ 60%. In no case was there an effect of ocean acidification (OA) upon respiration (dark- or light-dependent) for any of the phylotypes examined. Our observations suggest that OA might preferentially select among free-living populations of Symbiodinium, with implications for future symbioses that rely on algal acquisition from the environment (i.e., horizontal transmission). Furthermore, the carbon environment within the host could differentially affect the physiology of different Symbiodinium phylotypes. The range of responses we observed also highlights that the choice of species is an important consideration in OA research and that further investigation across phylogenetic diversity, for both the direction of effect and the underlying mechanism(s) involved, is warranted.本研究探究了升高的二氧化碳分压（pCO2）对共生藻属（Symbiodinium）4种系统型（ITS2型A1、A13、A2及B1）的光合作用与生长的影响。共生藻是一类多样性丰富的甲藻类群，无论在自由生活状态还是共生状态下，均对刺胞动物的存活至关重要，因此是一类极具研究价值的模式甲藻类群。 共生藻对升高pCO2的响应具有显著的系统型特异性。当二氧化碳分压翻倍时，A1与B1系统型基本不受影响；与之相反，A13的生长速率与A2的光合能力均提升了约60%。 在所检测的全部系统型中，海洋酸化（OA）对其呼吸作用（包括暗呼吸与光依赖呼吸）均未产生显著影响。 本研究结果表明，海洋酸化可能会对共生藻的自由生活种群产生定向选择效应，这对未来依赖从环境中获取藻类（即水平传播）的共生关系具有重要启示。此外，宿主体内的碳环境可对不同共生藻系统型的生理过程产生差异化影响。 本研究观测到的多样响应范围也凸显出，在海洋酸化研究中，实验物种的选择是一项关键考量因素；同时，针对效应方向与潜在作用机制，开展覆盖系统发育多样性的进一步研究均具有必要性。