12月16日，国际著名杂志Science在线刊登了加拿大和美国研究人员的最新研究成果“A Coherent Signature of Anthropogenic Nitrogen Deposition to Remote Watersheds of the Northern Hemisphere。”，研究证实在化肥之前很久人类已经在固氮了。
过去曾经有这样一个时期，其间氮仅能被某些能够打破氮原子间强有力的三键的微生物所利用。 新的研究显示，人类打断了这一自然氮循环的时间可早至一个世纪之前，在1895年左右。 Gordon Holtgrieve及其同事知道，自工业化前以来，人类的活动可能使得排入到生物圈的活性氮的量增加了一倍 --- 大多是通过使用内燃机和富含氮的肥料使然。 然而，在分析了整个北半球数个原始湖泊的沉积物核心中发现的同位素之后，这些研究人员发现，甚至在肥料生产变得普遍之前很久，人类的活动即造成了生物圈中氮的显著增加。 当与如今化肥生产所引起的直接溢流相比时，这些氮水平的升高相对较小。 但是，它们可能来自焚烧煤渣，且它们可能足以大到影响整个北半球流域的氮平衡（主要为生产力），时间如今已经超过一个世纪。 一则由James Elser撰写的相关的观点栏目更为详细地解释了这些发现。（生物谷Bioon.com）
doi:10.1126/science.1212267
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A Coherent Signature of Anthropogenic Nitrogen Deposition to Remote Watersheds of the Northern Hemisphere
Gordon W. Holtgrieve1,*, Daniel E. Schindler1, William O. Hobbs2, Peter R. Leavitt3, Eric J. Ward4, Lynda Bunting3, Guangjie Chen5,6, Bruce P. Finney7, Irene Gregory-Eaves5, Sofia Holmgren8, Mark J. Lisac9, Peter J. Lisi1, Koren Nydick10, Lauren A. Rogers1, Jasmine E. Saros11, Daniel T. Selbie12, Mark D. Shapley7, Patrick B. Walsh9, Alexander P. Wolfe13
Humans have more than doubled the amount of reactive nitrogen (Nr) added to the biosphere, yet most of what is known about its accumulation and ecological effects is derived from studies of heavily populated regions. Nitrogen (N) stable isotope ratios (15N:14N) in dated sediments from 25 remote Northern Hemisphere lakes show a coherent signal of an isotopically distinct source of N to ecosystems beginning in 1895 ± 10 years (±1 standard deviation). Initial shifts in N isotope composition recorded in lake sediments coincide with anthropogenic CO2 emissions but accelerate with widespread industrial Nr production during the past half century. Although current atmospheric Nr deposition rates in remote regions are relatively low, anthropogenic N has probably influenced watershed N budgets across the Northern Hemisphere for over a century.
