土壤铵态氮中氮稳定同位素丰度测定的两种前处理方法比较
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摘要
为了建立一种更准确、更快速的土壤铵态氮中氮稳定同位素丰度测定的前处理方法,分别采用扩散法和N_2O产生法进行前处理,通过稳定同位素质谱仪(Flash HT-IRMS)和气体预浓缩-稳定同位素质谱仪(PreCon-IRMS)分析了硫酸铵参比溶液和不同类型稻田土壤浸提液铵态氮中氮稳定同位素丰度。结果表明,采用扩散法和N_2O产生法测定硫酸铵参比溶液,均能获得较好的氮同位素分析精度,精密度分别小于0.5%和0.2%。但扩散法前处理过程中存在氮同位素分馏现象,需要通过标准曲线对测试结果进行校正。而对于不同类型稻田土壤浸提液铵态氮中氮稳定同位素丰度的测定,采用N_2O产生法结合PreCon-IRMS的分析方法所获得分析结果的准确度和精密度均优于扩散法结合Flash HT-IRMS的分析方法。另外,改进后的N_2O产生法结合辅助的全自动微量氮转化-N_2O发生装置可以实现对土壤浸提液铵态氮的在线批量前处理,分析时间短、样品消耗量少,仅需10μg的氮量。因此,针对土壤中微量铵态氮中氮稳定同位素丰度测定,采用N_2O产生法结合Precon-IRMS的分析方法比扩散法结合Flash HT-IRMS的分析方法更具有优势。
In order to establish more accurately and rapid pretreatment method for the nitrogen stable isotope analysis of soil ammonium nitrogen, diffusion and N_2O produced method were compared, and combined with two commercially available equipment's, i.e., elemental analyzer-isotope ratio mass spectrometer(Flash HT-IRMS) and trace gas preconcentration-stable isotope mass spectrometry(PreCon-IRMS), respectively, for the analysis of the nitrogen stable isotope abundance inammonium sulfate reference solutions and soil ammonium nitrogen extracted from different paddy soil samples. The stable isotope measurement results showed that both the diffusion and N_2O produced method coupled IRMS analytical systems were able to provide good analytical data for ammonium sulfate reference solutions in accuracy with precision of superior to 0.5% and 0.2%, respectively. However, there was a nitrogen isotope fractionation accrued in the diffusion-treated process, and the test results needed to be corrected by a standard curve. At the same time, the ~(15)N-stable isotope abundance in ammonium nitrogen extracted from different paddy soils were determined by diffusion and N_2O produced method. The comparison of the analytical data from the two analytical methods indicated that N_2O produced method coupled with PreCon-IRMS provided better nitrogen stable isotope data in reproducibility and accuracy than the data obtained by the other method. In addition, through the auxiliary automatic trace nitrogen conversion-N_2O generated device, nitrogen stable isotope abundance of soil ammonium nitrogen could be simultaneously analysis online in batch process, and the pretreatment analysis time was short, the sample consumption was small, only need 10 μg N for one sample(<5 mL soil extract solution). Therefore, for the analysis of nitrogen isotopes in micro-amounts of soil ammonium, the N_2O produced method coupled with PreCon-IRMS analysis method has more advantages than the diffusion method coupled Flash HT-IRMS analysis method.
In order to establish more accurately and rapid pretreatment method for the nitrogen stable isotope analysis of soil ammonium nitrogen, diffusion and N_2O produced method were compared, and combined with two commercially available equipment's, i.e., elemental analyzer-isotope ratio mass spectrometer(Flash HT-IRMS) and trace gas preconcentration-stable isotope mass spectrometry(PreCon-IRMS), respectively, for the analysis of the nitrogen stable isotope abundance inammonium sulfate reference solutions and soil ammonium nitrogen extracted from different paddy soil samples. The stable isotope measurement results showed that both the diffusion and N_2O produced method coupled IRMS analytical systems were able to provide good analytical data for ammonium sulfate reference solutions in accuracy with precision of superior to 0.5% and 0.2%, respectively. However, there was a nitrogen isotope fractionation accrued in the diffusion-treated process, and the test results needed to be corrected by a standard curve. At the same time, the ~(15)N-stable isotope abundance in ammonium nitrogen extracted from different paddy soils were determined by diffusion and N_2O produced method. The comparison of the analytical data from the two analytical methods indicated that N_2O produced method coupled with PreCon-IRMS provided better nitrogen stable isotope data in reproducibility and accuracy than the data obtained by the other method. In addition, through the auxiliary automatic trace nitrogen conversion-N_2O generated device, nitrogen stable isotope abundance of soil ammonium nitrogen could be simultaneously analysis online in batch process, and the pretreatment analysis time was short, the sample consumption was small, only need 10 μg N for one sample(<5 mL soil extract solution). Therefore, for the analysis of nitrogen isotopes in micro-amounts of soil ammonium, the N_2O produced method coupled with PreCon-IRMS analysis method has more advantages than the diffusion method coupled Flash HT-IRMS analysis method.
引文
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[11] KEENEY D R,BREMNER J M.Determination and isotope-ratio analysis of different forms of nitrogen in soils:6.mineralizable nitrogen[J].Soil Science Society of America Journal,1967,31(1):34-39.
[12] LAUGHLIN R J,STEVENS R J,ZHUO S.Determining nitrogen-15 in ammonium by producing nitrous oxide[J].Soil Science Society of America Journal,1997,61(2):462-465.
[13] STEVENS R J,LAUGHLIN R J.Determining nitrogen-15 in nitrite or nitrate by producing nitrous oxide[J].Soil Science Society of America Journal,1994,58:1 108-1 116.
[2] ROBINSON D.δ15N as an integrator of the nitrogen cycle[J].Trends in Ecology & Evolution,2001,16(3):153-162.
[3] 袁红朝,葛体达,陈晓娟,张丽萍,王久荣.稳定同位素质谱技术在生态系统氮素循环中的应用[J].质谱学报,2015,36(1):91-96.YUAN Hongzhao,GE Tida,CHEN Xiaojuan,ZHANG Liping,WANG Jiurong.Application of stable isotope ratio mass spectrometry in the ecology of nitrogen cycle[J].Journal of Chinese Mass Spectrometry Society,2015,36(1):91-96(in Chinese).
[4] FRANCIS STUART C,PAMELA A M,HAROLD A M.Principles of terrestrial ecosystem ecology[M].Springer,2011.
[5] 黄莉,王建伟,吴运泽,夏文倩,余莉,付帅,杨再婷.黔东南州稻田土壤硝态氮和铵态氮含量评价[J].安徽农业科学,2017,45(5):96-98.HUANG Li,WANG Jianwei,WU Yunze,XIA Wenqian,YU Li,FU Shuai,YANG Zaiting.Evaluation of soil nitrate nitrogen and ammonium nitrogen in rice fields of qiandongnan prefecture[J].Journal of Anhui Agricultural Sciences,2017,45(5):96-98(in Chinese).
[6] 贺纪正,张丽梅.土壤氮素转化的关键微生物过程及机制[J].微生物学通报,2013,40(1):98-108.HE Jizheng,ZHANG Limei.Key processes and microbial mechanisms of soil nitrogen transformation[J].Microbiology,2013,40(1):98-108(in Chinese).
[7] 曹亚澄,钟明,龚华,陆国兴.N2O 产生法测定土壤无机态氮15N丰度[J].土壤学报,2013,50(1):113-119.CAO Yacheng,ZHONG Ming,GONG Hua,LU Guoxing.Determining 15N abundance in ammonium,nitrate and nitrite in soil by measuring nitrous oxide produced[J].Acta Pedologica Sinica,2013,50(1):113-119(in Chinese).
[8] LORY J A,RUSSELLE M P.Evaluation of a diffusion method for preparing low-nitrogen samples for nitrogen-15 analysis[J].Soil Science Society of America Journal,1994,58(5):1 400-1 404.
[9] HERMAN D J,BROOKS P D,ASHRAF M,AZAM F,MULVANEY R L.Evaluation of methods for nitrogen analysis of inorganic nitrogen in soil extracts.Ⅱ.Diffusion methods[J].Communications in Soil Science and Plant Analysis,1995,26(11/12):1 675-1 685.
[10] MACKOWN C T,BROOKS P D,SMITH M S.Diffusion of nitrogen-15 kjeldahl digests for isotope analysis[J].Soil Science Society of America Journal,1987,51(1):87-90.
[11] KEENEY D R,BREMNER J M.Determination and isotope-ratio analysis of different forms of nitrogen in soils:6.mineralizable nitrogen[J].Soil Science Society of America Journal,1967,31(1):34-39.
[12] LAUGHLIN R J,STEVENS R J,ZHUO S.Determining nitrogen-15 in ammonium by producing nitrous oxide[J].Soil Science Society of America Journal,1997,61(2):462-465.
[13] STEVENS R J,LAUGHLIN R J.Determining nitrogen-15 in nitrite or nitrate by producing nitrous oxide[J].Soil Science Society of America Journal,1994,58:1 108-1 116.