Influence Factors Of Nitrogen Fertilization On Soil Greenhouse Gas Emissions In Wheat Field

The increase of greenhouse gas（GHGs）emissions restricts the sustainable development of the global natural ecological environment,which has become a major topic of common concern in many disciplines.Research on farmland soil GHGs emissions and their associated influencing factors could provide a theoretical basis for farmland soil GHGs emissions’reduction and mitigation of the greenhouse effect.The main conclusions are as follows:（1）Nitrogen（N）fertilization significantly promoted the emissions of CO₂ and N₂O from the wheat field.The impact of N fertilization on CO₂ emission was different in the growth and fallow period.Drought-resistant wheat variety could resist the dramatic increase of CO₂emission caused by N fertilization under high or low precipitation.When precipitation was low,the cumulative CH₄ uptake of drought-resistant wheat varieties was significantly higher than that of upland varieties,and the response of upland varieties’cumulative N₂O emission to N fertilization was higher than that of drought-resistant varieties with the increase of precipitation.On the basis of ensuring the yield,180 kg N hm^-2 fertilizer application is more reasonable.The contribution rates of CO₂,CH₄,and N₂O to global warming potential are82.3%,-0.7%,and 18.4%,respectively.The temperature sensitivity index Q10 of soil emissions of CO₂ and N₂O is reduced by N fertilization.（2）The soil profile of the wheat fields showed CO₂ and N₂O emissions,and CH₄ absorbed.Compared with 180 kg N hm^-2 treatment,360 kg N hm^-2 treatment could inhibit the CO₂ flux in 0-20 cm soil layer during the growth period,but promoted in the fallow period.N fertilization significantly increased N₂O diffusion flux in the soil profile,and 360 kg N hm^-2treatment significantly increased N₂O emission flux in the 20-60 cm soil layer during the growth period.CO₂ and N₂O emissions in soil profiles are significantly affected by seasonal temperature changes,soil water content has a greater impact on CH₄ oxidation.（3）Soil enzyme activity decreased with the increase in soil depth,and soil profile enzyme activities was regulated by crop growth,nitrogen application,and soil profile depth.In the soil without nitrogen treatment,more nutrients will be allocated to the enzyme synthesis process.N fertilization will lead to microbial carbon restriction,and excessive N fertilization will aggravate this restriction in the deep soil.Soil acidification caused by N fertilization may affect soil catalase activity to a certain extent.（4）CO₂ and N₂O emissions in each soil layer were significantly affected by soil temperature,and soil water content was negatively correlated with GHGs flux.The fluxes of CO₂,N₂O,and CH₄ were all regulated by the activity of CBH.The response of GHGs flux in soil profile to N fertilization was greatly influenced by biological factors,soil MBC and wheat root biomass were the most important factors affecting the response of GHGs fluxes to N fertilization.Among soil physicochemical properties,the response of CO₂ and CH₄ to N application was greatly affected by SOC and DOC,while the response of N₂O to N fertilization was greatly affected by DOC and NO₃^-.（5）The Meta-analysis showed that N fertilization promoted CO₂ flux,but excess nitrogen fertilization reduced CO₂ emission.N fertilization always promoted N₂O emission,but reduced CH₄ uptake in deep soil.Soil physical properties have a great influence on the change of CO₂ flux,while soil chemical properties have a great influence on N₂O and CH₄.Soil NH₄⁺,NO₃^-,and temperature are the most important factors affecting the response rate of CO₂ flux to nitrogen fertilization,and N fertilization mainly affects the effect of N₂O flux rate through soil changing SOC,NH₄⁺,and TN.The soil profile oxygen content was an important factor affecting the response of CH₄ to nitrogen fertilization.The application of organic fertilizer can significantly reduce the diffusion flux of GHGs,while the combined application of organic fertilizer and inorganic fertilizer can effectively reduce the CO₂ emission from the soil profiles,promote the uptake of CH₄ in agroecosystems,and reduce the loss of soil carbon.