Study On The Soil Nitrous Oxide Emission And Production In A Riparian Zone Of The Three Gorges Reservoir

Nitrous oxide（N₂O）plays a significant role in climate change,with soil being its primary source.The exchange of N₂O between soil and the atmosphere is a crucial process,encompassing both the production and consumption of this potent greenhouse gas.Therefore,we urgently need to accurately measure soil N₂O flux,adopt effective methods to quantify the contribution of major microbial sources,and explore the microbial mechanism of the corresponding processes.This will enable us to control the emission of N₂O.In this study,we focused on the water-level fluctuation zone of typical tributaries in the Three Gorges Reservoir.The research was divided into three parts:（1）Investigating the effects of different spatio-temporal scales and land use patterns on soil N₂O flux through in-situ static chamber-gas chromatography;（2）Studying the main production process of soil N₂O under varying soil water content using the isotopomer method;and（3）Comparing the results of isotopomer and Quantitative Real-time PCR（q PCR）to reveal the mechanism of N₂O production,and analyzing the expression of functional genes and microorganism activity in nitrification and denitrification processes.The main findings of this study can be summarized as follows:（1）The variations in soil N₂O flux at the soil-air interface in the Three Gorges Reservoir were analyzed.Monthly variations of N₂O flux were significant in 2014,2016,and 2020,but not in 2022.N₂O flux varied rapidly in early summer and autumn,with the highest N₂O flux observed in 2016.At microscale,N₂O flux showed a high degree of heterogeneity,but there was no significant difference in N₂O flux at different elevations.Moreover,land use had a significant effect on soil N₂O flux,with the highest N₂O flux observed in corn fields,followed by flooded paddy systems,and the lowest in grasslands and peanut fields.Regression analysis revealed that soil temperature,moisture,and soil available nitrogen（NH₄⁺and NO₃^-）were the main factors affecting soil N₂O emissions.（2）The study revealed that theδ¹⁵N^αandδ¹⁵N^βfractionation of N₂O varied under different soil water contents,leading to variations inδ¹⁵N^bulkand site preference（SP）.During the incubation period,the denitrification process was the main source of N₂O in the flooding treatment,while nitrification was the main source in the 20%GWC treatment.Further analysis showed that N₂O reduction occurred differently in the two treatments during the incubation period.N₂O reduction lasted throughout the incubation period in the 20%GWC treatment,while it occurred from the second to fourth day in the flooding treatment.Therefore,SP alone cannot be used to determine the main sources of N₂O.（3）Our study demonstrated that the combination of SP and q PCR provided a complementary approach for identifying N₂O sources under different soil water contents,which further confirmed the reliability of using SP to analyze the sources of N₂O.Specifically,the expression of nir S gene indicated that denitrification dominated N₂O production in the 20%GWC treatment,while the expression of AOB amo A gene indicated nitrification as the main source in the flooding treatment.By integrating abundance and SP data,more accurate assessments of N₂O production and reduction processes and the relative contributions of major microorganisms can be obtained.