Doubling of marine dinitrogen-fixation rates based on direct measurements
Doubling of marine dinitrogen-fixation rates based on direct measurements
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DOI：
10.1038/nature11338
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发表时间：
2012-08-16
期刊：
影响因子：
64.8
通讯作者：
LaRoche, Julie
中科院分区：
文献类型：
--
作者：
Grosskopf, Tobias;Mohr, Wiebke;LaRoche, Julie
生物固氮是海洋氮的最大输入，因此对海洋的氮存量和初级生产力具有重要的控制作用（1-3）。来自海洋沉积物的氮同位素数据表明，海洋氮的存量在过去3,000年中一直保持平衡（参考文献4）。然而，根据直接测量结果，很难得出一个平衡的海洋氮收支，因为氮的损失超过了固氮的增益约200 TgNyr（-1）（参考文献5、6）。在这里，我们提供了来自大西洋的数据，并表明最广泛使用的测量海洋N-2固定率的方法（7）相对于新开发的方法（8）低估了N-2固定微生物（固氮生物）的贡献。利用分子技术定量固氮生物特定分支的丰度，并与N-15（2）掺入颗粒有机物的速率平行，我们认为，用已建立的方法（7）和新方法8测量的N-2固定速率之间的差异可能与固氮生物群落的组成有关。我们的数据表明，在以束毛藻为主的地区，所建立的方法平均低估了62%的N-2固定率。我们还发现，新开发的方法产生的N-2-固定率高于6倍以上，从建立的方法时，单细胞，共生蓝藻和C-变形菌占主导地位的固氮群落。根据在大西洋测得的平均面积率，我们计算出全流域的N-2固定率为14 +/- 1 Tg N yr（-1）和24 +/- 1 Tg N yr（-1）的既定方法和新方法，分别。如果我们的研究结果可以外推到其他海洋盆地，这表明直接测量得出的全球海洋N-2固定率可能从103 +/- 8 Tg N yr（-1）增加到177 +/- 8 Tg N yr（-1），并且除束毛藻之外的N-2固定剂的贡献比以前认为的要重要得多。
Biological dinitrogen fixation provides the largest input of nitrogen to the oceans, therefore exerting important control on the ocean's nitrogen inventory and primary productivity(1-3). Nitrogen-isotope data from ocean sediments suggest that the marine-nitrogen inventory has been balanced for the past 3,000 years (ref. 4). Producing a balanced marine-nitrogen budget based on direct measurements has proved difficult, however, with nitrogen loss exceeding the gain from dinitrogen fixation by approximately 200 TgNyr(-1) (refs 5, 6). Here we present data from the Atlantic Ocean and show that the most widely used method of measuring oceanic N-2-fixation rates(7) underestimates the contribution of N-2-fixing microorganisms (diazotrophs) relative to a newly developed method(8). Using molecular techniques to quantify the abundance of specific clades of diazotrophs in parallel with rates of N-15(2) incorporation into particulate organic matter, we suggest that the difference between N-2-fixation rates measured with the established method(7) and those measured with the new method8 can be related to the composition of the diazotrophic community. Our data show that in areas dominated by Trichodesmium, the established method underestimates N-2-fixation rates by an average of 62%. We also find that the newly developed method yields N-2-fixation rates more than six times higher than those from the established method when unicellular, symbiotic cyanobacteria and c-proteobacteria dominate the diazotrophic community. On the basis of average areal rates measured over the Atlantic Ocean, we calculated basin-wide N-2-fixation rates of 14 +/- 1 Tg N yr(-1) and 24 +/- 1 Tg N yr(-1) for the established and new methods, respectively. If our findings can be extrapolated to other ocean basins, this suggests that the global marine N-2-fixation rate derived from direct measurements may increase from 103 +/- 8 Tg N yr(-1) to 177 +/- 8 Tg N yr(-1), and that the contribution of N-2 fixers other than Trichodesmium is much more significant than was previously thought.