Alfred-Wegener-Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany.
Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Schleusenstraße 1, 26382 Wilhelmshaven, Germany.
Sci Total Environ. 2024 May 20;926:171971. doi: 10.1016/j.scitotenv.2024.171971. Epub 2024 Mar 26.
Phototrophic protists are a fundamental component of the world's oceans by serving as the primary source of energy, oxygen, and organic nutrients for the entire ecosystem. Due to the high thermal seasonality of their habitat, temperate protists could harbour many well-adapted species that tolerate ocean warming. However, these species may not sustain ecosystem functions equally well. To address these uncertainties, we conducted a 30-day mesocosm experiment to investigate how moderate (12 °C) and substantial (18 °C) warming compared to ambient conditions (6 °C) affect the composition (18S rRNA metabarcoding) and ecosystem functions (biomass, gross oxygen productivity, nutritional quality - C:N and C:P ratio) of a North Sea spring bloom community. Our results revealed warming-driven shifts in dominant protist groups, with haptophytes thriving at 12 °C and diatoms at 18 °C. Species responses primarily depended on the species' thermal traits, with indirect temperature effects on grazing being less relevant and phosphorus acting as a critical modulator. The species Phaeocystis globosa showed highest biomass on low phosphate concentrations and relatively increased in some replicates of both warming treatments. In line with this, the C:P ratio varied more with the presence of P. globosa than with temperature. Examining further ecosystem responses under warming, our study revealed lowered gross oxygen productivity but increased biomass accumulation whereas the C:N ratio remained unaltered. Although North Sea species exhibited resilience to elevated temperatures, a diminished functional similarity and heightened compositional variability indicate potential ecosystem repercussions for higher trophic levels. In conclusion, our research stresses the multifaceted nature of temperature effects on protist communities, emphasising the need for a holistic understanding that encompasses trait-based responses, indirect effects, and functional dynamics in the face of exacerbating temperature changes.
光养性原生生物是世界海洋的基本组成部分，它们是整个生态系统能量、氧气和有机养分的主要来源。由于它们栖息地的季节性高温，温带原生生物可能拥有许多适应能力强的物种，可以耐受海洋变暖。然而，这些物种可能无法同等地维持生态系统功能。为了解决这些不确定性，我们进行了为期 30 天的中观实验，以研究与环境条件（6°C）相比，适度（12°C）和较大（18°C）的变暖如何影响北海春季水华群落的组成（18S rRNA 宏条形码）和生态系统功能（生物量、总氧气生产力、营养质量 - C:N 和 C:P 比）。我们的结果表明，变暖驱动了主要原生生物群的变化，在 12°C 时甲藻繁盛，在 18°C 时硅藻繁盛。物种的响应主要取决于物种的热特征，间接的温度对摄食的影响不太重要，而磷则起着关键的调节作用。Phaeocystis globosa 物种在低磷酸盐浓度下表现出最高的生物量，并且在两种变暖处理的一些重复中相对增加。与此一致的是，C:P 比随着 P. globosa 的存在而变化大于温度。在变暖条件下进一步研究生态系统的响应，我们的研究表明，总氧气生产力降低，但生物量积累增加，而 C:N 比保持不变。尽管北海物种对高温表现出了恢复力，但功能相似性降低和组成变异性增加表明，对于更高营养级别的生态系统可能会产生影响。总之，我们的研究强调了温度对原生生物群落影响的多方面性质，强调需要从整体上理解，包括基于特征的响应、间接效应和功能动态，以应对不断加剧的温度变化。
