Nitrogen fertilization raises CO2 efflux from inorganic carbon: A global assessment
Nitrogen fertilization raises CO2 efflux from inorganic carbon: A global assessment
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DOI：
10.1111/gcb.14148
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发表时间：
2018-07
影响因子：
11.6
通讯作者：
Kazem Zamanian;M. Zarebanadkouki;Y. Kuzyakov
中科院分区：
文献类型：
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作者：
Kazem Zamanian;M. Zarebanadkouki;Y. Kuzyakov
氮肥施用是全球不可或缺的农业措施，关乎全球一半人口的生存。土壤中的氮转化（例如硝化作用）以及植物对氮的吸收会释放质子，加剧土壤酸化。在含碳酸盐的土壤（74.9亿公顷；约占全球陆地表面积的54%）中中和这种酸性会导致每施用1千克氮释放相当于0.21千克碳的二氧化碳。我们在此首次提出含碳酸盐土壤酸化这一问题，并评估了土壤上层1米深度内成土碳酸盐和原生碳酸盐释放的全球二氧化碳量。基于全球氮肥施用图和含碳酸钙土壤的分布，我们计算出此类土壤酸化每年释放的二氧化碳量为7.48×10¹²克碳/年。这种持续的二氧化碳释放水平至少在土壤施用氮肥期间将保持不变。此外，我们估计在碳酸钙中和的同一过程中，但涉及酸性土壤施石灰的情况下，每年约有273×10¹²克二氧化碳 - 碳被释放。这两个二氧化碳源相当于全球化石燃料燃烧二氧化碳排放量的3%，或土地利用变化产生二氧化碳量的30%。重要的是，土地利用变化后二氧化碳释放的持续时间通常仅为1 - 3十年，之后土壤中会达到新的碳平衡。相比之下，只要施用氮肥直至碳酸钙完全中和，由碳酸钙酸化释放的二氧化碳就无法达到平衡。由于土壤中如果存在碳酸钙，其含量几乎是无限的，它们的完全溶解和二氧化碳释放将需要数百年甚至数千年。这强调了防止施氮肥土壤酸化的必要性，这是抑制数千年二氧化碳向大气排放的有效策略。因此，氮肥施用应严格根据植物需求计算，应避免过度施肥，这不仅是因为氮是局部和区域富营养化的源头，还因为全球酸化会导致二氧化碳持续释放。
Nitrogen (N) fertilization is an indispensable agricultural practice worldwide, serving the survival of half of the global population. Nitrogen transformation (e.g., nitrification) in soil as well as plant N uptake releases protons and increases soil acidification. Neutralizing this acidity in carbonate‐containing soils (7.49 × 109 ha; ca. 54% of the global land surface area) leads to a CO2 release corresponding to 0.21 kg C per kg of applied N. We here for the first time raise this problem of acidification of carbonate‐containing soils and assess the global CO2 release from pedogenic and geogenic carbonates in the upper 1 m soil depth. Based on a global N‐fertilization map and the distribution of soils containing CaCO3, we calculated the CO2 amount released annually from the acidification of such soils to be 7.48 × 1012 g C/year. This level of continuous CO2 release will remain constant at least until soils are fertilized by N. Moreover, we estimated that about 273 × 1012 g CO2‐C are released annually in the same process of CaCO3 neutralization but involving liming of acid soils. These two CO2 sources correspond to 3% of global CO2 emissions by fossil fuel combustion or 30% of CO2 by land‐use changes. Importantly, the duration of CO2 release after land‐use changes usually lasts only 1–3 decades before a new C equilibrium is reached in soil. In contrast, the CO2 released by CaCO3 acidification cannot reach equilibrium, as long as N fertilizer is applied until it becomes completely neutralized. As the CaCO3 amounts in soils, if present, are nearly unlimited, their complete dissolution and CO2 release will take centuries or even millennia. This emphasizes the necessity of preventing soil acidification in N‐fertilized soils as an effective strategy to inhibit millennia of CO2 efflux to the atmosphere. Hence, N fertilization should be strictly calculated based on plant‐demand, and overfertilization should be avoided not only because N is a source of local and regional eutrophication, but also because of the continuous CO2 release by global acidification.