氮氧双同位素模型在土壤氮溯源的应用

Abstract: 【Objective】 The objective of this paper is to understand the contribution of microbial processes to N2O production and its changing rules under different water contents to provide a theoretical basis for reducing agricultural N2O emissions.

【Method】A microcosm experiment was performed to investigate the effects of different water-filled pore space on N2O emissions and isotopic signatures (δ15Nbulk, δ18O and nitrogen isotopomer site preference of N2O) of soil at Shunyi district, Beijing. The studycombined stable isotope technique and gas inhibitor method to analyze N2O flux and its isotope signatures that emitted from soil. The

experiment was set up three different water content levels, including 67%, 80% and 95% WFPS, and with three inhibitor levels,(without C2H2, with 0.1% (V/V) C2H2 and with 10% (V/V) C2H2). After two hours incubation, the soil samples were collected todetermine the concentrations of NH+4 -N and NO-3-N. The gas samples were collected to determine the isotope signatures, and the two end-members mixing model was applied to quantify the respective contributions of microbial processes to N2O production. 

【Result】According to the incubation of the soil, the weighted average N2O flux of 95%, 80% and 67% WFPS were 1.17, 0.27 and 0.08mgN·kg-1·d-1, respectively, and the N2O emissions of 95% WFPS were significantly higher than that of both 80% and 67% WFPS, as well as the N2O emissions of 80% WFPS were significantly higher than that of 67% WFPS. The cumulative emissions of (N2O+N2)in 95%, 80% and 67% WFPS were 18.05%, 5.27%, and 1.24% of initial mineral nitrogen, respectively, over the entire incubation period. The cumulative emissions of (N2O+N2) were 19.61, 5.72 and 1.35 mgN·kg-1, respectively; the initial content of NH+4-N+NO-3-N was 108.62 mgN·kg-1. Compared with 67% WFPS, the cumulative (N2O+N2) emissions of 95% and 80% WFPS increased 13.53 and 3.24 times, respectively. The cumulative emissions of (N2O+N2) in 95% WFPS was 2.43 times greater than that of 80% WFPS.The values of reduced NH+

4 -N+NO-3-N as gaseous nitrogen increased with the increase of the water content. The weighted averageδ15Nbulk values varied from -42.93‰ to -4.07‰, and the higher level of soil water content showed significantly higher N2O emissions. 10% (V/V) C2H2 would inhibit the reduction of N2O to N2. The δ18O values with 10% (V/V) C2H2 were significantly smaller than that of with 0.1% (V/V) C2H2 in three water content levels. And the ratio of N2O/(N2O+N2) reduced with the increase

of soil moisture. Multiple N2O processes occurred simultaneously in all treatments. The values of SP increased during the initial four days and then decreased gradually with incubation time. The SP values of 67%WFPS treatment at the first two days ranged from 6.74‰ to 12.04‰, and the contribution of denitrification to N2O production was from 56.36% to 66.15%, suggesting that denitrification was the dominant microbial process, then the contribution of nitrification (55.78%-1) to N2O production became greater. The weighted average SP value was 10.26‰ in 80% WFPS treatment, indicating denitrification (40.90%-74.04%) was the major N2O production process. There were larger SP values in 95% WFPS treatment with 10% (V/V) C2H2 in the first seven incubation days, ranged from 7.61‰ to 21.11‰. Compared with 0.1% (V/V) C2H2, the weighted average SP values of N2O under

95%, 80% and 67% WFPS treatments with 10% (V/V) C2H2 produced from soil reduced by 0.10, 0.33 and 0.06 times respectively.

【Conclusion】 The increase of soil water content promotes N2O emission, and the 95% WFPS treatment showed the highest N2O emissions. In the 67% WFPS treatment, the initial stage of N2O emission was dominated by denitrification, followed by

nitrification. Denitrification was the dominate process in 80% WFPS treatment and nitrification was the dominate process in 95% WFPS treatment.