The nitrogen legacy: emerging evidence of nitrogen accumulation in anthropogenic landscapes
The nitrogen legacy: emerging evidence of nitrogen accumulation in anthropogenic landscapes
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DOI：
10.1088/1748-9326/11/3/035014
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发表时间：
2016-03
影响因子：
6.7
通讯作者：
C. V. Stechow;J. Minx;K. Riahi;J. Jewell;D. McCollum;M. Callaghan;J. Leon;A. Grinham;J. Church;B. Gibbes;C. Woodroffe;J. Canadell
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作者：
C. V. Stechow;J. Minx;K. Riahi;J. Jewell;D. McCollum;M. Callaghan;J. Leon;A. Grinham;J. Church;B. Gibbes;C. Woodroffe;J. Canadell
流域和全球尺度的氮（N）收支表明，人类景观中的大部分N盈余并没有到达沿海海洋。虽然有一个普遍的共识，这'失踪' N要么退出景观通过反硝化或保留在流域内的硝酸盐或有机N，这些池和通量的相对大小受到相当大的不确定性。我们的研究，第一次，提供了直接的，大规模的证据N积累在农业土壤的根区，可能占大部分的“失踪N”在质量平衡研究中确定。我们分析了整个密西西比河流域（MRB）2069个地点的长期土壤数据（1957-2010），揭示了农田中25-70 kg ha−1 yr−1的氮积累，在流域尺度上总计3.8 ± 1.8 Mt yr−1。然后，我们开发了一个简单的建模框架，以捕捉集约农业下的氮素消耗和积累动态。使用该模型，我们表明，所观察到的积累土壤有机氮（SON）在MRB超过30年的时间（142 Tg N）将导致一个生态地球化学滞后时间为35年的99%的遗产SON，即使完全停止施肥。通过证明农业土壤可以作为一个净氮汇，目前的工作作出了重要贡献，对关闭流域氮预算。
Watershed and global-scale nitrogen (N) budgets indicate that the majority of the N surplus in anthropogenic landscapes does not reach the coastal oceans. While there is general consensus that this ‘missing’ N either exits the landscape via denitrification or is retained within watersheds as nitrate or organic N, the relative magnitudes of these pools and fluxes are subject to considerable uncertainty. Our study, for the first time, provides direct, large-scale evidence of N accumulation in the root zones of agricultural soils that may account for much of the ‘missing N’ identified in mass balance studies. We analyzed long-term soil data (1957–2010) from 2069 sites throughout the Mississippi River Basin (MRB) to reveal N accumulation in cropland of 25–70 kg ha−1 yr−1, a total of 3.8 ± 1.8 Mt yr−1 at the watershed scale. We then developed a simple modeling framework to capture N depletion and accumulation dynamics under intensive agriculture. Using the model, we show that the observed accumulation of soil organic N (SON) in the MRB over a 30 year period (142 Tg N) would lead to a biogeochemical lag time of 35 years for 99% of legacy SON, even with complete cessation of fertilizer application. By demonstrating that agricultural soils can act as a net N sink, the present work makes a critical contribution towards the closing of watershed N budgets.