Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies
Distinct nitrogen cycling and steep chemical gradients in Trichodesmium colonies
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DOI：
10.1038/s41396-019-0514-9
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发表时间：
2020-02-01
期刊：
影响因子：
11
通讯作者：
Ploug, Helle
中科院分区：
文献类型：
--
作者：
Klawonn, Isabell;Eichner, Meri J.;Ploug, Helle
束毛藻是海洋生态系统中一种重要的固氮蓝藻。最近的核酸分析表明，束毛藻菌落与其多样的外生体支持各种氮（N）的转换以外的N-2固定。然而，这些转换率和浓度梯度的N化合物在束毛藻殖民地仍然在很大程度上没有得到解决。我们结合同位素示踪剂孵育，微轮廓和数字建模，探索碳固定，氮循环过程以及氧气，铵和硝酸盐浓度梯度在个别现场采样束毛藻殖民地。菌落净自养，与碳和N-2固定主要发生在白天。10%的固定N被释放为铵12小时孵育后。硝化作用是不可检测的，但硝酸盐的消耗高时，添加硝酸盐。消耗的硝酸盐部分还原为铵，而反硝化作用是微不足道的。因此，潜在的氮转化网络的特点是固定的氮增益和再循环过程，而不是反硝化。菌落内的氧浓度类似于60-200%的空气饱和度。此外，我们的模型预测陡峭的浓度梯度，高达6倍高的铵浓度，和硝酸盐耗尽相比，在殖民地中心的环境海水。这些梯度创造了一个化学异质性的微环境，大概促进不同的微生物代谢毫米大小的束毛藻菌落。
Trichodesmium is an important dinitrogen (N-2)-fixing cyanobacterium in marine ecosystems. Recent nucleic acid analyses indicate that Trichodesmium colonies with their diverse epibionts support various nitrogen (N) transformations beyond N-2 fixation. However, rates of these transformations and concentration gradients of N compounds in Trichodesmium colonies remain largely unresolved. We combined isotope-tracer incubations, micro-profiling and numeric modelling to explore carbon fixation, N cycling processes as well as oxygen, ammonium and nitrate concentration gradients in individual field-sampled Trichodesmium colonies. Colonies were net-autotrophic, with carbon and N-2 fixation occurring mostly during the day. Ten percent of the fixed N was released as ammonium after 12-h incubations. Nitrification was not detectable but nitrate consumption was high when nitrate was added. The consumed nitrate was partly reduced to ammonium, while denitrification was insignificant. Thus, the potential N transformation network was characterised by fixed N gain and recycling processes rather than denitrification. Oxygen concentrations within colonies were similar to 60-200% air-saturation. Moreover, our modelling predicted steep concentration gradients, with up to 6-fold higher ammonium concentrations, and nitrate depletion in the colony centre compared to the ambient seawater. These gradients created a chemically heterogeneous microenvironment, presumably facilitating diverse microbial metabolisms in millimetre-sized Trichodesmium colonies.