氮有几种同位素,质量数为12—17。在农业中最重要的两种,是放射性核素~(13)N(其半衰期为10.05分,几乎限制了它的使用)和稳定性核素~(15)N。~(13)N 还没有应用于非豆科联合共生固氮的研究。应用~(15)N 的优点是无放射性、安全、相对地说较为便宜。0.5—1%~(15)N 富集度用于一年的实验是足够的。高价的测定同位素比值质谱计已逐步被专门分析~(15)N 且精确度达0.005原子%(~(15)N原子%)的廉价仪器所代替。在应用~(15)N 准确说明固氮实验结果时,了解同位素的各项术语及与固氮相关的计算是必 There are several isotopes of nitrogen, with a mass of 12-17. The two most important species in agriculture are radionuclide ~ (13) N (with a half-life of 10.05, which almost limits its use) and the stable nuclide ~ (15) N. ~ (13) N has not been applied to the symbiotic nitrogen fixation of non-legumes. The advantage of using ~ (15) N is that it is non-radioactive, safe, and relatively inexpensive. 0.5-1% ~ (15) N enrichment for a year of experiments is sufficient. The expensive isotope ratio mass spectrometer has been replaced by inexpensive instruments that specifically analyze ~ (15) N with an accuracy of 0.005 atomic% (~ (15) N atomic%). When applying ~ (15) N to accurately describe the results of nitrogen fixing experiments, it is essential to understand the terms of isotopes and the calculations related to nitrogen fixation