N₂O Emissions And Its Controlling Factors From The Saline-alkali Lands In The Zhalong Wetland

With the concentration of greenhouse gases in the atmosphere continues to increase,climate warming has become the world's generally concerned environmental issue.N2O is an important greenhouse gas with significant warming effects,which has long-term and potential impacts on the global climate and environment.Wetlands are important source or sink of N2O.The changes of physicochemical properties such as soil temperature,humidity,pH and soil carbon and nitrogen content will affect microbial-mediated nitrification and denitrification,thus affecting N2O emissions of wetlands.As an important component of wetlands,the study of N2O emission in saline-alkali wetlands has great significance in exploring the nitrification mechanism of N2O production and assessing the role of saline-alkali wetlands in the greenhouse effect.This experiment studied the N2O emission characteristics of saline-alkali wetlands and the effects of environmental factors and nitrification on their N2O emissions.As the typical saline-alkali wetland in northern China,the soil temperature of Zhalong Reed Wetland showed a decreasing trend,and the average soil temperature was 6.2°C?20.2°C.With the depth of the soil increased,the soil temperature gradually decreased.In each observational study,the temperature of different soil layers showed significant differences(P<0.05).At the same time,the wetland continued to accumulate water in mid-August,and the water table depth ranged from 3.3 cm to 27.0 cm.And the soil pH was between 7.73 and 8.90,suggesting the soil is alkaline.Meanwhile,the TOC and TN contents were 27.45?51.85 g.kg-1 and 0.80?2.05 g.kg-1,and the NH4+-N and NO3-N contents were 0.48?2.23 mg·kg-1 and 0.42-0.71 mg kg-1.Except for the NO3-N content,the other three contents gradually decreased with the increase of soil depth.The TOC,TN and NH4+-N contents of different soil layers showed significant differences(P?0.05),while there was no difference in the NO3--N content.By the method of static chamber-gas chromatography,this paper studied the N2O fluxes and environmental factors of the typical Zhalong reed wetland during the growing season.The results suggested that the N2O fluxes showed the trend of decreasing volatility,with the maximum value in the middle July.The mean flux of N2O was(37.49±15.75)?g·(m2·h)-1,suggesting that the typical Zhalong reed wetland was the source of nitrous oxide.The N2O fluxes showed significantly positive correlation with soil temperature at different depths(P<0.05),and the impact of upper soil temperature on N2O flux was higher than that of deep soil.In the flooding period,the relationship between N2O fluxes and water table depth was negatively correlated(P<0.05).However,the correlation between N2O fluxes and pH value at different depths was not significant(P>0.05).Meanwhile,the TOC and TN contents were lower,and the N^O fluxes were significantly positively correlated with the NH4+-N contents in the 0-40 cm soil layer(P<0.05),but not related to the NO3-N contents.Nitrification is stronger than denitrification.In addition,the fluctuation range of potential ammonia oxidation rate(NO2-/dry soil)was 4.40?13.45 ?g·h)-1,with the highest value in the middle July.The overall trend of change was basically consistent with N2O emissions.There was a significant positive correlation between ammonia oxidizing bacteria activity and soil temperature in 0-20 cm layer(P<0.01),and a significant positive correlation with the NH4+-N contents(P<0.05).By the further analysis,the activity of ammonia oxidizing bacteria also showed significantly linear positive-correlation with the N2O fluxes(P<0.001),which indicated that the release of N2O in saline-alkali wetlands was greatly affected by nitrification.