气候变化领域集成服务门户

Isotopocule analysis by quantum cascade laser spectrometry (QCL) is a promising approach for in situ, real-time tracking of the biological sources of soil N2O emissions. However, background atmospheric N2O is an important source of variability in the measurement of isotopocule ratios (i.e.,(NNO)-N-14-N-15-O-16/(NNO)-N-14-N-14-O-16 and (NNO)-N-15-N-14-O-16/(NNO)-N-14-N-14-O-16) of gas samples. Here, a method based on Keeling plot for determining the intramolecular N-15 distribution in N2O is introduced. The sensitivity and reliability of this method are examined against N2O of known N-15 site preference (SP), and N2O produced from fungal and bacterial isolates, soils with different moisture contents and organic amendments, and a soil chamber under field conditions. The isotopocules of N2O determined by standard gases supported that the Keeling plot method was more reliable than the averaging method. Using this method, SP of N2O was greater in fungal than bacterial denitrifiers, as well as in soil at 60% water filled pore space (WFPS) than 80-100% WFPS. This method also determined that the SP of N2O was distinct between soils of different substrate complexity. Further, we observed a N2O SP between - 18.9 parts per thousand and 2.2% in a soil flux chamber deployed in a corn field after 2 d of rainfalls that is consistent with the SP of N2O produced from bacterial denitrification and nitrifier denitrification. Our data demonstrate that this Keeling plot method provides accurate discrimination of biological sources when N2O is analyzed by the QCL system. (C) 2016 Elsevier Ltd. All rights reserved.