Study On N₂O And NO Fluxes And Their Influencing Factors In Saline-Alkali Soil

Nitrous oxide and nitric oxide are important active gases in the atmosphere,which are closely related to a series of environmental problems such as greenhouse effect,ozone layer depletion and regional air pollution.Soil is a non negligible emission source of N₂O and NO.At present,there are many studies on N₂O and NO fluxes in non saline alkali soils,but there is still a lack of sufficient understanding of N₂O and NO fluxes in saline alkali soil.Therefore,in this study,three kinds of soils with different saline alkali degrees(non saline alkali soil,moderately saline alkali soil and saline soil)were selected.By undisturbed soil column culture experiment,the N₂O and NO flux characteristics of soils with different saline alkali degrees were observed,using static dark chamber-gas chromatography technique and dynamic dark chamber-chemiluminescence analysis technique,and the N₂O and NO emission laws of saline alkali soils were revealed.The effects of soil salinity on soil N₂O and NO fluxes were investigated,and the regulatory effects of physical and chemical factors such as soil temperature and humidity on N₂O and NO fluxes were clarified.The main results are as follows:(1)In the stage of humidity and temperature control,the increase of salinity promoted the emission of N₂O.The mean N₂O emission fluxes of soils with different salinity and alkalinity were:non saline alkali soil(0.65±0.07?g N m^-2h^-1)-2h^-1)-2h^-1).In the process of freeze-thaw cycle,the mean N₂O emission fluxes of soils with different saline alkali degrees were 6.58±0.53,5.21±0.41 and 5.13±0.41?g N m^-2h^-1 in non saline alkali soil,moderately saline alkali soil and saline soil,respectively.During the freeze-thaw cycle,N₂O emission was low and even N₂O uptake occurred during the freezing period,but N₂O emission was high during the ablation period.(2)In the stage of controlled temperature and humidity,the saline-alkali soil was weak emission source of NO.The mean NO emission fluxes of the soil were 0.57±0.10,0.45±0.02 and 0.48±0.04?g N m^-2h^-1 in non saline alkali soil,moderately saline alkali soil and saline soil,respectively.In the process of freeze-thaw cycle,the mean NO emission fluxes of the soil with different saline alkali degrees were1.62±0.58,3.42±0.41and 3.10±0.58?g N m^-2h^-1 in non saline alkali soil,moderately saline alkali soil and saline soil,respectively.The mean NO flux in moderately saline alkali soil and saline soil was significantly higher than that in non saline alkali soil.(3)In the first stage of temperature and humidity control,with the increase of salinity,soil N₂O flux increased while NO flux decreased.The intensity of soil nitrification decreased with the increase of soil salinity,and the denitrification strengthened.In the second stage of temperature and humidity control,the molar ratio of NO to N₂O flux was less than 1under the condition of medium and high precipitation.Soil denitrification played a leading role in the production of NO and N₂O.During the freeze-thaw cycle,most molar ratio of NO and N₂O fluxes in the soil during the freezing period were much greater than 1,and the production of NO and N₂O were dominated by nitrification.The occurrence frequencies of molar ratio higher than 1 and less than 1 were similar during the ablation period,and the contribution of nitrification and denitrification to the production of NO and N₂O were similar.(4)The effect of soil temperature on N₂O flux was strong while weak on NO flux.Soil temperature significantly affected N₂O fluxes in non saline alkali soil and saline soil(p<0.05).However,only when the precipitation was 15 mm,soil temperature had a significant effect on NO flux in non saline alkali soil(p<0.05).The effects of soil moisture on N₂O and NO fluxes were very significant under three culture temperatures in non saline alkali soil(p<0.01),but the effect was weak in moderately saline alkali soil and saline soil.(5)DOC had significant effects on soil N₂O flux(p<0.01)and NO flux(p<0.05).The effect was negative on the former while positive on the latter.Soil nitrate had no significant effect on both of them.And soil ammonium significantly promoted N₂O flux(p<0.05).(6)Soil conductivity had a significant effect on both soil N₂O and NO flux(p<0.05).Soil conductivity had a positive effect on N₂O flux and a negative effect on NO flux.The p H had no significant effect on both soil N₂O and NO fluxes(p>0.05).