我组方运霆研究员的在 Environmental Science & Technology 发表文章：Fang YT, Koba K, Makabe A, Zhu FF, Fan SY, Liu XY, Yoh M. Low δ¹⁸O values of nitrate produced from nitrification in temperate forest soils. Environmental Science & Technology,2012.46(16): 8723-8730. 

　　文章链接：http://pubs.acs.org/doi/abs/10.1021/es300510r 

　　Analyses of δ¹⁸O of nitrate (NO₃^–) have been widely used in partitioning NO₃^– sources. However the δ¹⁸O value of NO₃^–produced from nitrification (microbial NO₃^–) is commonly estimated using the δ¹⁸O of environmental water and molecular oxygen in a 2:1 ratio. Here our laboratory incubation of nine temperate forest soils across a 1500 m elevation gradient demonstrates that microbial NO₃^– has lower δ¹⁸O values than the predicted using the 2:1 ratio (by 5.2–9.5‰ at low elevation sites), in contrast to previous reports showing higher δ¹⁸O values (up to +15‰) than their predicted values. Elevated δ¹⁸O values of microbial NO₃^– were observed at high elevation sites where soil was more acidic, perhaps due to accelerated O-exchange between nitrite, an intermediate product of nitrification, and water. Lower δ¹⁸O of microbial NO₃^– than the predicted and from previous observations suggests that the contribution of anthropogenic N inputs, such as fertilizer and atmospheric deposition, to a given ecosystem and the progress of denitrification in nitrogen removal are greater than we know. More than half of the δ¹⁸O of stream NO₃^– lower than the predicted value along the elevation gradient also indicate the impropriety using the 2:1 ratio for differentiating NO₃^– sources.