Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: Results from 15N tracer experiments
Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: Results from 15N tracer experiments
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DOI：
10.1016/j.soilbio.2009.01.017
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发表时间：
2009-04
影响因子：
9.7
通讯作者：
R. Russow;C. F. Stange;H. Neue
中科院分区：
文献类型：
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作者：
R. Russow;C. F. Stange;H. Neue
最近的研究已经证明，土壤亚硝酸盐是了解土壤中N气体（NO，N2 O，N2）产生的关键因素。NO被广泛认为是反硝化过程中N2 O形成的一个必不可少的中间产物。然而，与本土土壤的研究不能确认NO作为N2 O的前体，和田间试验主要揭示了铵硝化作为NO的来源。假设构建，NO在土壤中的有限扩散是这种矛盾的原因。为了验证这一扩散限制假说，并验证亚硝酸盐和NO作为游离中间体在原生土壤中，我们进行了通流（He/O2大气）15 N示踪实验，使用黑土土壤中的实验设置自由扩散限制。在81 h的培养试验中，采用同位素动力学方法对3个相关的无机氮库（铵态氮、亚硝酸盐和硝酸盐）进行了15 N标记。在实验过程中，O2分压分四步从20%降低到约0%。随着O2分压的降低，NO的净排放量增加到3.7μgNkg−1h− 1。由于特殊的实验设置，几乎没有气体扩散的障碍，只能观察到非常低的N2 O排放。正如预期的那样，底物铵、硝酸盐和亚硝酸盐的含量在孵育时间内几乎保持恒定。亚硝酸盐的15 N丰度揭示了高周转率。铵态氮的硝化作用对亚硝酸盐总生成量的贡献约为0.001。88%，但随着O2分压的下降，迅速下降到零。值得注意的是，已经在20%O2的高分压下，12%的亚硝酸盐由硝酸盐反硝化产生，并且在严格的厌氧条件下，它增加到100%。亚硝酸盐至少存在于两个独立的内源性库中，每个库由铵的硝化或硝酸盐的反硝化提供。实验清楚地表明，亚硝酸盐几乎是100%的直接前体的NO形成在厌氧以及有氧条件下。在严格的厌氧条件下（0- 0.2%O2），排放的N2 O仅约100%来自NO，这证明NO是反硝化作用形成N2 O的游离中间体。据我们所知，这是第一次在原生土壤中检测到NO作为反硝化过程中N2 O形成的游离中间产物。这些结果清楚地验证了“扩散限制”假说。
Recent research has proven soil nitrite to be a key element in understanding N-gas production (NO, N2O, N2) in soils. NO is widely accepted to be an obligatory intermediate of N2O formation in the denitrification pathway. However, studies with native soils could not confirm NO as a N2O precursor, and field experiments mainly revealed ammonium nitrification as the source of NO. The hypothesis was constructed, that the limited diffusion of NO in soil is the reason for this contradiction. To test this diffusion limitation hypothesis and to verify nitrite and NO as free intermediates in native soils we conducted through-flow (He/O2atmosphere)15N tracer experiments using black earth soil in an experimental set up free of diffusion limitation. All of the three relevant inorganic N soil pools (ammonium, nitrite, nitrate) were15N labelled in separate incubation experiments lasting 81h based on the kinetic isotope method. During the experiments the partial pressure of O2was decreased in four steps from 20% to about 0%. The net NO emission increased up to 3.7μgNkg−1h−1with decreasing O2partial pressure. Due to the special experimental set up with little to no obstructions of gas diffusion, only very low N2O emission could be observed. As expected the content of the substrates ammonium, nitrate and nitrite remained almost constant over the incubation time. The15N abundance of nitrite revealed high turnover rates. The contribution of nitrification of ammonium to the total nitrite production was approx. 88% under strong aerobic soil conditions but quickly decreased to zero with declining O2partial pressure. It is remarkable that already under the high partial pressure of 20% O212 % of nitrite is generated by nitrate denitrification, and under strict anaerobic conditions it increases to 100%. Nitrite is present in two separate endogenous pools at least, each one fed by the nitrification of ammonium or the denitrification of nitrate. The experiments clearly revealed that nitrite is almost 100% the direct precursor of NO formation under anaerobic as well as aerobic conditions. Emitted N2O only originated to about 100% from NO under strict anaerobic conditions (0–0.2% O2), providing evidence that NO is a free intermediate of N2O formation by denitrification. To the best of our knowledge this is the first time that NO has been detected in a native soil as a free intermediate product of N2O formation at denitrification. These results clearly verify the “diffusion limitation” hypothesis.