Phenotypic Plasticity of Southern Ocean Diatoms: Key to Success in the Sea Ice Habitat?

Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species’ known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem.硅藻是南大洋生态系统的核心营养与能量来源。包括硅藻在内的微藻可合成脂质、蛋白质与碳水化合物等生物大分子，用于自身生长、繁殖以及对所处环境条件的适应。本研究表明，南大洋三种关键硅藻物种——圆柱拟脆杆藻（Fragilariopsis cylindrus）、简单角毛藻（Chaetoceros simplex）与弯拟菱形藻（Pseudo-nitzschia subcurvata）——在应对海冰季节性形成与消融过程中所经历的盐度与温度变化时，表现出了表型可塑性（phenotypic plasticity）。就生物大分子组成变化而言，表型可塑性的程度具有显著的物种特异性，且与各物种在海冰、融水以及远洋生境中的已知分布与丰度模式相符，这表明表型可塑性可能是极地海洋环境极端多变性所筛选保留的适应性性状。我们认为，气候变化背景下硅藻大分子组成的改变以及物种优势度的更替，有可能改变整个南大洋生态系统的营养与能量通量。