Warming Iron-Limited Oceans Enhance Nitrogen Fixation and Drive Biogeographic Specialization of the Globally Important Cyanobacterium Crocosphaera
Warming Iron-Limited Oceans Enhance Nitrogen Fixation and Drive Biogeographic Specialization of the Globally Important Cyanobacterium Crocosphaera
复制标题
DOI：
10.3389/fmars.2021.628363
复制
发表时间：
2021-02
期刊：
影响因子：
--
通讯作者：
Nina Yang;C. Merkel;Yu-An Lin;N. Levine;N. Hawco;Hai-Bo Jiang;Ping-Ping Qu-Ping;Michelle A. DeMers-Michelle-A.-DeMer
中科院分区：
文献类型：
--
作者：
Nina Yang;C. Merkel;Yu-An Lin;N. Levine;N. Hawco;Hai-Bo Jiang;Ping-Ping Qu-Ping;Michelle A. DeMers-Michelle-A.-DeMer
营养贫乏的亚热带海洋环流的初级生产力取决于来自固氮剂的新氮输入，这些固氮剂将惰性二氮气体转化为生物可利用的形式。温度和铁 (Fe) 的可用性限制了海洋固氮，并且由于人为海洋变暖，两者都在发生变化。我们研究了全球重要的海洋固氮剂 Crocosphaera watsonii 在其整个温度范围内的生理反应，作为铁利用率的函数。在其温度范围的下限，即 22 至 27°C，鳄鱼球菌的生长、固氮和氮特异性铁利用效率（N-IUE，mol N 固定小时–1 mol Fe–1）随着温度的升高而增加。在 27°C 的最佳生长温度下，铁限制条件下的 N-IUE 比铁充足条件下高 66%，表明低铁利用率提高了代谢效率。然而，鳄鱼球菌的生长和功能会从 27°C 降至 32°C，预计未来热带海洋中的这种温度将会不断增加。总而言之，这表明鳄鱼非常适合在规定限度内的铁有限的温暖水域。在 IPCC RCP 8.5 变暖情景下纳入这些结果的模型预测，到 2100 年，鳄鱼球藻 N-IUE 可能净增加 47%，特别是在高纬度水域。这些结果与已发表的另一种主要固氮剂（Trichodesmium）的反应形成鲜明对比，预测 N-IUE 在低纬度热带水域中增加最多。这些模型预测，鳄鱼球菌和Trichodesmium N-IUE对未来铁有限海洋变暖的不同反应可能会增强它们目前对全球海洋固氮的贡献，其速率分别增加约91%和约22%，从而改变它们对海洋新生产的相对重要性，并加剧它们的区域差异。因此，温度和铁的相互作用可能会深刻地改变公海地区氮生物地球化学和初级生产力的现有范式。
Primary productivity in the nutrient-poor subtropical ocean gyres depends on new nitrogen inputs from nitrogen fixers that convert inert dinitrogen gas into bioavailable forms. Temperature and iron (Fe) availability constrain marine nitrogen fixation, and both are changing due to anthropogenic ocean warming. We examined the physiological responses of the globally important marine nitrogen fixer, Crocosphaera watsonii across its full thermal range as a function of iron availability. At the lower end of its thermal range, from 22 to 27°C, Crocosphaera growth, nitrogen fixation, and Nitrogen-specific Iron Use Efficiencies (N-IUEs, mol N fixed hour–1 mol Fe–1) increased with temperature. At an optimal growth temperature of 27°C, N-IUEs were 66% higher under iron-limited conditions than iron-replete conditions, indicating that low-iron availability increases metabolic efficiency. However, Crocosphaera growth and function decrease from 27 to 32°C, temperatures that are predicted for an increasing fraction of tropical oceans in the future. Altogether, this suggests that Crocosphaera are well adapted to iron-limited, warm waters, within prescribed limits. A model incorporating these results under the IPCC RCP 8.5 warming scenario predicts that Crocosphaera N-IUEs could increase by a net 47% by 2100, particularly in higher-latitude waters. These results contrast with published responses of another dominant nitrogen fixer (Trichodesmium), with predicted N-IUEs that increase most in low-latitude, tropical waters. These models project that differing responses of Crocosphaera and Trichodesmium N-IUEs to future warming of iron-limited oceans could enhance their current contributions to global marine nitrogen fixation with rates increasing by ∼91 and ∼22%, respectively, thereby shifting their relative importance to marine new production and also intensifying their regional divergence. Thus, interactive temperature and iron effects may profoundly transform existing paradigms of nitrogen biogeochemistry and primary productivity in open ocean regimes.