利用膜进样质谱仪测定水稻土几种厌氧氮转化速率

为了在同一体系下区分和测定水稻土反硝化、厌氧氨氧化(Anammox)和硝酸根异化还原成铵(DNRA)过程发生速率和相互关系,并获取近似原位情况下的净脱氮速率,本研究通过将~(15)NH_4~+化学氧化法测定DNRA速率和添加尿素模拟原位土柱测定净脱氮速率与膜进样质谱法(MIMS)进行联用,完善了一套基于膜进样质谱法(MIMS)的稻田硝态氮转化测定方法体系,利用该方法测定了5种典型的水稻土辽宁营口(YK)、江苏宜兴(YX)、浙江金华(JH)、广西桂林(GL)和四川广安(GA)]的反硝化、Anammox、DNRA和净脱氮4种氮转化速率。结果显示:基于MIMS的方法体系可实现对水稻土中反硝化、Anammox、DNRA和净脱氮速率的测定,5种水稻土反硝化、Anammox、DNRA和净脱氮速率范围分别为(358.63±25.37)～(479.96±22.12)、(-14.81±0.22)～(5.29±1.22)、(25.76±12.71)～(109.87±3.88)g N·hm~(-2)·h~(-1)和(33.33±11.16)～(72.74±14.18)g N·hm~(-2)·h~(-1),相关结果与其他方法研究结果具有可比性。相关性分析显示:水稻土NO_3~-、可溶性有机碳(DOC)和土壤Fe~(2+)含量是反硝化过程的主要限制因素;NO_3~-是Anammox的关键限制因素;而土壤DOC和Fe~(2+)含量是DNRA过程的主要限制因素。基于MIMS的方法体系可以在短时间内(1周)测定水稻土四种厌氧氮转化速率,且所需样品量低、精确度高,在稻田或湿地土壤厌氧氮转化过程研究中有很好的应用前景。

Measurement of denitrification, Anammox, DNRA rates, and net N2 flux in paddy soil using a membrane inlet mass spectrometer

Denitrification, anaerobic ammonium oxidation(Anammox), and dissimilatory nitrate reduction to ammonium(DNRA)are the three nitrate reduction processes that largely control the fate of chemical N fertilizers in flooded rice paddies. Previous studies related to the nitrate reduction process mainly focused on one or two independent processes(e.g., denitrification and Anammox), whereas a simultaneous investigation of denitrification, Anammox, and DNRA and their relative contributions to total nitrate removal is lacking. Because of methodological limitations, the near in situ measurement of net N₂ flux is also rare. In this study, using membrane inlet mass spectrometry(MIMS) combined with laboratory soil slurry-based ¹⁵N tracer and soil core incubation-based N₂/Ar techniques, denitrification, Anammox, DNRA,and net N₂ flux were investigated in five paddy soils collected from different rice regions of China(Yingkou, YK; Yixing, YX; Jinhua, JH; Guilin, GL; Guangan, GA). The measured rates of denitrification, Anammox, DNRA, and net N₂ flux across all paddy soils were(358.63±25.37)~(479.96±22.12),(-14.81±0.22)~(5.29±1.22)(, 25.76±12.71)~(109.87±3.88), and(33.33±11.16)~(72.74±14.18)g N·hm^-2·h^-1, respectively, which were comparable with previous studies. The soil NO₃^-, DOC(dissolved organic carbon), and Fe²⁺ contents were the three dominating factors affecting denitrification. By comparison, the Anammox rates only correlated with the soil NO₃^- content, whereas the DNRA rates closely related to the soil DOC and Fe²⁺ content. These results demonstrate that the MIMS combined with laboratory soil slurry-based ¹⁵N tracer and soil core incubation-based N₂/Ar techniques is a viable, rapid, and precise method for the measurement of denitrification, Anammox, DNRA rates, and net N₂ flux in flooded paddy soil, with an obvious advantage that a smaller sample size is required for determination compared to other methods.