Well Reinhard, Burkart Stefan, Giesemann Anette, Grosz Balázs, Köster Jan Reent, Lewicka-Szczebak Dominika
Thünen Institute of Climate-Smart Agriculture, Bundesallee 65, 38116, Braunschweig, Germany.
Rapid Commun Mass Spectrom. 2019 Mar 15;33(5):437-448. doi: 10.1002/rcm.8363.
Field measurement of denitrification in agricultural ecosystems using the N gas flux method has been limited by poor sensitivity because current isotope ratio mass spectrometry is not precise enough to detect low N fluxes in the presence of a high atmospheric N background. For laboratory studies, detection limits are improved by incubating soils in closed systems and under N -depleted atmospheres.
We developed a new procedure to conduct the N gas flux method suitable for field application using an artificially N -depleted atmosphere to improve the detection limit at the given precision of mass spectrometry. Laboratory experiments with and without N-labelling and using different flushing strategies were conducted to develop a suitable field method. Subsequently, this method was tested in the field and results were compared with those obtained from the conventional N gas flux method.
Results of the two methods were in close agreement showing that the denitrification rates determined were not biased by the flushing procedure. Best sensitivity for N + N O fluxes was 10 ppb, which was 80-fold better than that of the reference method. Further improvement can be achieved by lowering the N background concentration below the values established in the present study.
In view of this progress in sensitivity, the new method will be suitable to measure denitrification dynamics in the field beyond peak events.
使用N2O气体通量法对农业生态系统中的反硝化作用进行实地测量一直受到灵敏度低的限制，因为当前的同位素比率质谱法不够精确，无法在高大气氮背景下检测到低N2O通量。对于实验室研究，通过在封闭系统和贫氮气氛中培养土壤来提高检测限。
我们开发了一种新程序，使用人工贫氮气氛进行适合实地应用的N2O气体通量法，以在给定的质谱精度下提高检测限。进行了有无N标记以及使用不同冲洗策略的实验室实验，以开发一种合适的实地方法。随后，该方法在实地进行了测试，并将结果与传统N2O气体通量法获得的结果进行了比较。
两种方法的结果非常一致，表明所确定的反硝化速率不受冲洗程序的影响。对N2O + N2通量的最佳灵敏度为10 ppb，比参考方法高80倍。通过将氮背景浓度降低到本研究确定的值以下，可以实现进一步的改进。
鉴于灵敏度方面的这一进展，新方法将适用于测量田间峰值事件之外的反硝化动态。
