利用反硝化细菌法测试水体硝酸盐氮氧同位素

反硝化细菌方法作为测试硝酸盐氮氧同位素组成的最新方法,具有可测试低浓度水样、对样品无需特殊处理、不会交叉污染和需样量少等诸多优点而得到迅速发展。本研究率先在国内实验室利用反硝化细菌法成功测试了硝酸盐氮氧同位素组成,将经过5～10d培养的反硝化细菌Pseudomonas aureofaciens离心,然后将菌液浓缩5倍,再向顶空进样瓶注入3mL菌液,密封后利用高纯氮气吹扫3h以上,注入50nmolNO3-水样经过夜培养灭活后,使用TraceGasPre-concentrator-Isoprime测试N2O同位素组成,结果表明,重现性和测试精度与国际上类似研究接近。该方法的建立对于国内开展河流及湖泊(水库)、降水等氮的生物地球化学循环将起到促进作用。

Measurement of waters nitrate dual isotopes based on denitrifier method

Denitrifier method is a novel method for nitrogen and oxygen isotopic analysis of nitrate, which has many advantages, e.g., low nitrate water sample, simple pretreatment, no cross-contamination, and small volume water, and obtained rapid popularization. In this study, the method was first developed in China for nitrate isotopic measurement in our laboratory. The denitrifier (Pseudomonas aureofaciens) was grown in an amended medium of Tryptic Soy Broth. After 5-10 days culture, the cells were harvested and concentrated 5 folds, and split into 3 mL aliquots in 20 mL headspace vials. The vials were sealed and then purged for at least 3 h with high-purity N2 to ensure anaerobic condition. A sample amount corresponding to 50 nmol of nitrate was added to the sample vials, and cultured overnight to allow the complete conversion of NO3- to N2O. On the following day, 0.1-0.2 mL of 10 mol·L-1 NaOH was injected into the vials to lyse the bacterium and to scrub any CO2 gas. Simultaneous δ15N and δ18O analysis of the produced N2O was carried out by using a Trace Gas Pre-concentrator unit coupled to an IRMS instrument. The measured data showed good reproducibility and precision, in close with the similar international studies. The establishment of this method would promote our studies in nitrogen biogeochemical cycle in rivers and lakes (reservoirs) and in precipitation.