Molecular underpinnings and biogeochemical consequences of enhanced diatom growth in a warming Southern Ocean

The Southern Ocean (SO) harbours some of the most intense phytoplankton blooms on Earth. Changes in temperature and iron availability are expected to alter the intensity of SO phytoplankton blooms, but little is known about how environmental change will influence community composition and downstream biogeochemical processes. We performed experimental manipulations on surface ocean microbial communities from McMurdo Sound in the Ross Sea, with and without iron addition, at -0.5 °C, 3 °C, and 6 °C. We then examined nutrient uptake patterns as well as the growth and molecular responses of two dominant diatoms, Fragilariopsis and Pseudo-nitzschia, to these conditions. We found that nitrate uptake and primary productivity were elevated at increased temperature in the absence of iron addition, and were even greater at high temperature with added iron. Pseudo-nitzschia became more abundant under increased temperature without added iron, while Fragilariopsis required additional iron to benefit ...

南大洋（Southern Ocean, SO）孕育着地球上最为剧烈的浮游植物水华之一。温度与铁有效性的变化预计会改变南大洋浮游植物水华的强度，但目前学界对环境变化如何影响浮游植物群落组成及后续生物地球化学过程仍知之甚少。我们针对罗斯海麦克默多湾的表层海洋微生物群落开展了操控性实验，实验设置了-0.5 ℃、3 ℃、6 ℃三个温度梯度，并分别设置添加铁与不添加铁两组处理。随后我们分析了两种优势硅藻——脆杆藻属（Fragilariopsis）与拟菱形藻属（Pseudo-nitzschia）在上述实验条件下的营养盐摄取模式、生长情况及分子响应特征。研究结果显示，在不添加铁的条件下，硝酸盐摄取速率与初级生产力随温度升高而提升；而在添加铁的高温条件下，这两项指标的提升幅度更为显著。在不添加铁的升温条件下，拟菱形藻属的丰度显著升高；而脆杆藻属则需要额外添加铁才能获得生长收益……