The warming ocean is expected to be more phosphorus (P) limited due to increasing stratification. P is a major limiting nutrient of marine diazotrophs, while the interactive effect of temperature elevation and P limitation on marine unicellular diazotrophs is unknown. Here, we examined the physiology of a major unicellular diazotroph, Crocosphaera watsonii, grown under P-limited and P-replete conditions at 25°C, 28°C, and 31°C. Growth, N₂, and CO₂ fixation rates of C. watsonii increased with temperature under P limitation, and growth rates were similar between P-limited and P-replete treatments at 31°C. At high temperature, the P use efficiencies for N₂ and CO₂ fixation under P limitation were more than twice higher than under P-replete conditions. Expression of genes involved in P acquisition, intracellular recycling, and substitution in C. watsonii was upregulated at higher temperature under P limitation. These results suggest that P limitation in C. watsonii was relieved with elevated temperature through various temperature-dependent economic strategies on P metabolism. Through meta-analysis of a field data set using general additive model, we found that C. watsonii abundance was correlated mainly with temperature and phosphate, and predicted to increase significantly with further warming.

中文翻译：

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升高的温度减轻了海洋单细胞固氮蓝藻的磷限制

由于分层增加，预计变暖的海洋将受到更多的磷 (P) 限制。P是海洋固氮菌的主要限制性营养元素，而温度升高和P限制对海洋单细胞固氮菌的交互作用尚不清楚。在这里，我们检查了在 25°C、28°C 和 31°C 的 P 限制和 P 充足条件下生长的主要单细胞固氮菌Crocosphaera watsonii的生理学。在 P 限制条件下， C. watsonii的生长、N ₂和 CO ₂固定率随着温度的升高而增加，并且在 31°C 的 P 限制和 P 充足处理之间的生长速率相似。在高温下，P对N ₂和CO _{2的利用效率}P 限制下的固定比 P 充足条件下高两倍以上。在 P 限制下， C.watsonii中参与 P 获取、细胞内循环和替代的基因的表达在较高温度下上调。这些结果表明，通过对 P 代谢的各种温度依赖性经济策略，随着温度升高， C. watsonii中的 P 限制得到缓解。通过使用通用加性模型对现场数据集进行荟萃分析，我们发现C. watsonii丰度主要与温度和磷酸盐相关，并预测随着进一步变暖而显着增加。