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| Determination of 15N and 18O isotope abundance in the extractable soil nitrate by the denitrifier method |
| Received:April 19, 2016 |
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| KeyWord:denitrifier method;soil extract;nitrate;15N and 18O isotope abundance |
| Author Name | Affiliation | E-mail | | XU Chun-ying | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | | | LI Yu-zhong | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | liyuzhong@caas.cn | | LI Qiao-zhen | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | | | MAO Li-li | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | | | LIN Wei | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | | | QIANG Xiao-jing | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | | | ZHENG Qian | Key Laboratory of Dryland Agriculture, Ministry of Agriculture in China, Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural Sciences, Beijing 100081, China | |
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| Abstract: |
| A method has been established for determing simultaneously 15N and 18O isotope abundance in the extractable soil nitrate using denitrifier bacteria. The method was optimized by using 5000~8000 r·min-1 centrifugal rotational speed, purging 1 h with high pure N2, reducing the amounts of samples and improving the autosampler based on the preliminary findings. Analysis of international standard of USGS34 showed that the method presented better accuracy, precision, and stability. The standard deviations(SD) of δ15N and δ18O were 0.05‰~0.09‰ and 0.28‰~0.48‰ respectively in the same sample at the same time within 3 months. Additionally, the effects of some factors such as the extracting agents, storage condition and heating on δ15N and δ18O of soil nitrate were analyzed. The results showed that the extracted solution such as KCl or CaCl2 had no effect on the determination of δ15N and δ18O if sampling amount was small. Nevertheless, the significant difference would be found under bigger sampling amount with impure extracting agents. Moreover, the results also indicated that the cryopreservation method was better than the cold preservation for the δ15N and δ18O in the soil nitrate. Analysis of δ15N and δ18O should be finished as soon as possible; on the other hand, the soil extracted solution should be cryopreserved. No significant effect of the heat treatment was observed for δ15N values of USGS34 and IAEA-NO3. However, the raw δ18O values showed that there were significant differences in heating, and this caused oxygen isotopic fractionation. But no significant differences were observed for δ15N and δ18O in the extracted soil nitrate samples. Therefore, we suggested that the soil nitrate extracts can directly react with denitrifier in order to avoid the oxygen isotopic fractionation and save the test time. Based on these, 15N and 18O isotope abundance in the extractable soil nitrate under the different fertilizer fields were investigated by using this method. |
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