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Nitrous oxide (N2O) is an important greenhouse gas. High input of water and fertilizer in vegetable production results in large N2O emission. Though drip irrigation is the most commonly used irrigation method in vegetable production, it is still unclear how water and fertilizer interaction under drip irrigation affects N2O emission. Therefore, the objective of this study was to analyze the effects of different fertilizer treatments under drip irrigation on N2O emission and isotopic signatures, and thus provide a theoretical support for reducing N2O emission in vegetable production mainly driven by microbial activity that included Bacterial Nitrification (BN), Bacterial Denitrification (BD), Nitrifier Denitrification (ND), Fungal Denitrification (FD) and N2O reduction to N2. The study was conducted in at the environmental research station of the Chinese Academy of Agricultural Sciences, situated in the Shunyi District, Beijing, China (40°15′N, 116°55′E). The soil of the experiment field was classified as calcareous fluvo–aquic. The Chinese cabbage was sown on 7 August 2015. Under drip irrigation, four fertilizer treatments were evaluated, including inorganic NPK compound fertilizer (NPK), organic fertilizer of sheep manure (M), water-soluble fertilizer of amino acid (WS), and no-fertilizer (NF). Gas and soil samples were collected throughout the study phase. The concentration and isotopic signature values (δ15NbulkN2O and δ18ON2O of N2O), ammonium (NH4+) and nitrate (NO3-) content of soil, soil C/N, and yield of Chinese cabbage were analyzed. Net isotope effect between N2O and H2O and 15N site preference in N2O molecule (SP) were also analyzed and used to distinguish BN/FD and BD/ND and to calculate the extent of N2O reduction to N2. The results showed that the SP had significant positive correlation with both δ15NbulkN2O and δ18ON2O (P<0.01), and significant negative correlation with N2O emission fluxes (P<0.01) and Water Filled Pore Space (WFPS, P <0.05). It indicated that using SP vs. δ18ON2O to quantitatively analyze production and consumption pathways of N2O was feasible and water content significantly affected the activity of soil microorganisms. Under approximately 60% WFPS condition, for the NPK, M, WS and NF treatments, the N2O emission were 1 074, 146.5, 116.2 and 112.9 μg/(m²·h), respectively. The Nitrogen Use Efficiency (NUE) of the NPK, M and WS were 45.1%, 22% and 45.2%, respectively. The yield of Chinese cabbage of the NPK, M, WS and NF were 147.9, 116.5, 127.5 and 86.4 t/hm², respectively, and the contribution of nitrification were 38%, 46%, 54% and 49%, respectively, and the extent of N2O reduction were 14%, 71% 46%, and 70%, respectively. The water-soluble fertilizer treatment showed the highest NUE and relatively low N2O emission, and both inorganic fertilizer treatments showed the low extent of N2O reduction, which was unfavorable for reducing N2O emission during denitrification. In contrast, organic fertilizer treatment had the highest the extent of N2O reduction, which was the main pathway to reduce N2O emission during denitrification. Therefore, this study suggests that organic fertilizer may be used as the base fertilizer with water and fertilizer integration technology as a management practice during the growing season for reducing N2O emission and enhancing NUE. [ABSTRACT FROM AUTHOR]

The stable isotope ratio in human hair can be used to trace back the spatial and temporal information of human life. The construction of a comparable database of stable isotope ratio in Chinese human hair has a great significance for forensic science research and public security investigation. However, the interference of sample pretreatment and the difference of normalization methods affected the accuracy and reproducibility of hydrogen isotope ratio measurement and made it difficult to make comparison between laboratories. This research were based on the elemental analysis-isotope ratio mass spectrometer technic (EA-IRMS), and it systematically demonstrate the selection of hydrogen isotopic reference materials and the normalization method of hydrogen isotopic compositions to isotope reference scales. Firstly, six international reference materials (USGS42, USGS43, CBS, KHS, EMAP1 and EMAP2) were selected to evaluate their suitability. Then, according to the range of δ2H values (-55‰～-80‰) of Chinese human hair measured and reported in the literatures, three of them were selected, including the minimum, maximum and middle values of the samples. Finally, by comparing the six reference materials combinations (CBS/USGS42/USGS43, CBS/USGS42/EMA-P1, CBS/USGS42/KHS, EMA-P2/USGS42/USGS43, EMA-P2/USGS42/EMA-P1 and EMA-P2/USGS42/KHS), it is proved that the standard calibration curves fitting R2 (1.000 0±0.000 0, n=4) of USGS42, USGS43 and CBS combinations are the highest, and the coefficients (1.061 8±0.006 6, n=4) of them are the most stability than other combinations by utilizing linear regression of multiple-point normalization method. At the same time, two laboratories in Beijing and Shanghai were selected to carry out 35 repeated validations. The results show that the multiple-point normalization method of the standard combination has the highest fitting degree and good stability (R2≥0.999 7, n=35). It is suitable for the normalization method of hair δ2H and can be used as a recommended method for the construction of Chinese human hair δ2H database. The idea of selecting isotopic reference materials and the normalization method of hydrogen isotopic compositions to isotope reference scales can also provide reference for the establishment of other stable isotope ratio database. [ABSTRACT FROM AUTHOR]