Effects Of Atmospheric Nitrogen And Phosphorus Deposition On Greenhouse Gas Release From Soils In The Drawdown Zone Of The Three Gorges Reservoir Are

As the largest terrestrial ecosystem carbon pool,even slight mineralization of surface soil organic carbon may cause significant increases in atmospheric CO2 and CH4 concentrations,leading to a global temperature rise.Atmospheric nitrogen and phosphorus deposition is an important factor affecting the carbon cycle of terrestrial ecosystems.Human activities have led to a significant increase in atmospheric nitrogen and phosphorus deposition,and as the global population continues to expand and energy consumption further increases,global atmospheric nitrogen and phosphorus deposition will continue to intensify.Therefore,the impact of atmospheric nitrogen and phosphorus deposition on soil CO2 and CH4 release has become a focus of attention.The research on the response of soil CO2 and CH4 release to atmospheric nitrogen and phosphorus deposition mainly focuses on forest,grassland,and wetland ecosystems.Due to significant differences in soil properties among different ecosystems,different or even opposite conclusions have been drawn.To establish an effective evaluation model,more research is still needed on soil ecosystems.The water-level fluctuation zone is the boundary zone between aquatic and terrestrial ecosystems,which is affected by periodic fluctuations in water levels and is in a dry wet alternating environment.This special hydrological environment makes it an important source of global greenhouse gas emissions,but there are few reports on the response of soil CO2 and CH4 emissions in the subsidence zone to atmospheric nitrogen and phosphorus deposition.This study aims to investigate the response and key mechanisms of CO2 and CH4 release and temperature sensitivity to atmospheric nitrogen and phosphorus deposition in the soil of the Three Gorges Reservoir area’s subsidence zone using indoor cultivation methods.The research results are as follows:During the drying period:(1)The combined addition of nitrogen or nitrogen phosphorus significantly increased the content of soil ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3--N),dissolved organic nitrogen(DON),and microbial biomass nitrogen(MBN)(P<0.05),while there was no significant difference between phosphorus addition and the control(P>0.05).(2)Different nitrogen and phosphorus addition treatments did not significantly change the soil CO2 release rate and temperature sensitivity(Q10-CO2)of the entire subsidence zone(P>0.05),but the combined addition of nitrogen or nitrogen and phosphorus showed a decreasing trend.Soil acidification caused by nitrogen and phosphorus addition may be the reason for this result.On the one hand,with the joint addition of nitrogen or nitrogen phosphorus,the soil pH value is reduced,thereby reducing the content of dissolved organic carbon(DOC)or microbial biomass carbon(MBC)in the soil,thereby inhibiting the release rate of soil CO2.On the other hand,as the pH value decreases,Q10-CO2 is directly inhibited.During the flooding period:(1)The combined addition of nitrogen and phosphorus had no significant effect on the release rates of CO2 and CH4 in the soil of the entire subsidence zone(P>0.05).The soil acidification and increased NO3--N content caused by nitrogen and phosphorus addition may be the reasons for this result.On the one hand,the decrease in soil pH with the combined addition of nitrogen or nitrogen phosphorus reduces the content of DOC in the soil,or indirectly suppresses the rate of soil CO2 release by reducing MBC content.On the other hand,the reduced soil pH directly promotes the rate of CO2 release in the soil.For the release rate of soil CH4,on the one hand,the combined addition of nitrogen or nitrogen phosphorus promotes the release rate of soil CH4 by reducing soil pH value.On the other hand,the combined input of nitrogen or nitrogen phosphorus leads to an increase in NO3--N concentration in the soil,which inhibits the release rate of soil CH4.The combined effects of these two aspects may result in a non significant response of soil CO2 and CH4 release rates to the co addition of nitrogen and phosphorus.(2)The addition of nitrogen and phosphorus had no significant effect on the temperature sensitivity of soil CO2 and CH4 release in the entire subsidence zone(P>0.05).Correlation analysis showed that there was no significant correlation between Q10-CO2 and soil physicochemical properties(P>0.05).On the one hand,the decrease in soil pH caused by the combined addition of nitrogen or nitrogen phosphorus promotes the temperature sensitivity of soil CH4 release(Q10-CH4).On the other hand,the combined input of nitrogen or nitrogen phosphorus leads to an increase in NO3--N concentration in the soil,which inhibits Q10-CH4.The promotion and inhibition effects of pH decrease and NO3--N increase may lead to the lack of significant response of Q10CH4 to nitrogen and nitrogen phosphorus co input.This article studies the changes and underlying mechanisms of CO2 and CH4 release rates and temperature sensitivity in the soil of the Three Gorges Reservoir area under the background of atmospheric nitrogen and phosphorus deposition.The research results can provide a basic theoretical basis for predicting the impact of increased atmospheric nitrogen and phosphorus load on the greenhouse gas release in the soil of the Three Gorges Reservoir area.