Heterotrophic bacteria associated with microphytoplankton, particularly those colonizing the phycosphere, are major players in the remineralization of algal-derived carbon. Ocean warming might impact dissolved organic carbon (DOC) uptake by microphytoplankton-associated bacteria with unknown biogeochemical implications. Here, by incubating natural seawater samples at three different temperatures, we analysed the effect of experimental warming on the abundance and C and N uptake activity of Rhodobacteraceae and Flavobacteria, two bacterial groups typically associated with microphytoplankton. Using a nano-scale secondary ion mass spectrometry (nanoSIMS) single-cell analysis, we quantified the temperature sensitivity of these two taxonomic groups to the uptake of algal-derived DOC in the microphytoplankton associated fraction with 13 C-bicarbonate and 15 N-leucine as tracers. We found that cell-specific 13 C uptake was similar for both groups (~0.42 fg C h-1 μm-3 ), but Rhodobacteraceae were more active in 15 N-leucine uptake. Due to the higher abundance of Flavobacteria associated with microphytoplankton, this group incorporated fourfold more carbon than Rhodobacteraceae. Cell-specific 13 C uptake was influenced by temperature, but no significant differences were found for 15 N-leucine uptake. Our results show that the contribution of Flavobacteria and Rhodobacteraceae to C assimilation increased up to sixfold and twofold, respectively, with an increase of 3°C above ambient temperature, suggesting that warming may differently affect the contribution of distinct copiotrophic bacterial taxa to carbon cycling.

中文翻译：

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温暖藻圈：温度对两种嗜营养细菌类群对硅藻来源碳的利用的差异影响。

与微浮游植物相关的异养细菌，特别是定植于藻圈的细菌，是藻类碳再矿化的主要参与者。海洋变暖可能会影响浮游植物相关细菌对溶解有机碳（DOC）的吸收，而对生物地球化学的影响未知。在这里，通过在三个不同温度下孵育天然海水样品，我们分析了实验性变暖对红细菌和黄细菌（两个通常与浮游植物相关的细菌）的丰度以及碳和氮吸收活性的影响。使用纳米级二次离子质谱（nanoSIMS）单细胞分析，我们以13 C-碳酸氢盐和15 N-亮氨酸为示踪剂，定量了这两个分类组对藻类浮游植物相关部分中藻类DOC吸收的温度敏感性。我们发现两组的细胞特异性13 C摄取相似（〜0.42 fg C h-1μm-3），但红景天科在15 N-亮氨酸摄取中更活跃。由于与浮游植物相关的黄细菌含量较高，因此该组的碳含量比红细菌科高出四倍。细胞特异性13 C摄取受温度影响，但15 N-亮氨酸摄取无明显差异。我们的结果表明，随着环境温度升高3°C，黄细菌和红细菌科对C同化的贡献分别增加了六倍和两倍。