Effects Of Land Use Change On Soil N₂O And CH₄ Emissions In Taihu Lake Area

Global warming is a major challenge which affects human's survival and development today.Methane(CH₄)and nitrous oxide(N₂O)are the two most important greenhouse gases after carbon dioxide(CO₂).Soil is an important source of atmospheric CH₄ and N₂O.With the advancement of the historical process,the land use types in the Taihu Lake region has undergone an evolution from natural wetlands to rice-wheat rotation fields,and then from rice-wheat rotation fields to greenhouse vegetable fields.This evolution process reflects the increase in the degree of intensification of land use and the increase in farmers'income,but its impact on the greenhouse effect is still unknown.In this paper,we selected typical natural wetlands,rice-wheat rotation fields,and greenhouse vegetable fields in the Taihu Lake region.Through2 years of field in-situ observation experiments,the effects of land use change on greenhouse gas CH₄ and N₂O emissions and their comprehensive greenhouse effect were explored.The main research conclusions are as follows:Land use changes have significantly reduced CH₄ emissions.The cumulative emissions of CH₄ from natural wetlands,rice-wheat rotation fields,and greenhouse vegetable fields during the entire observation period were 970.66 kg C ha^-1,896.71 kg C ha^-1,and-71.23 kg C ha^-1,respectively.CH₄ emissions from natural wetlands have obvious seasonal changes,and emissions are mainly concentrated in summer.The CH₄ emissions of rice-wheat rotation fields are mainly concentrated in the flooding period of the paddy fields,and the CH₄ emissions of the wheat season are relatively low.Greenhouse vegetable fields show a state of absorbing CH₄,which is a sink of atmospheric CH₄.Land use changes have significantly increased N₂O emissions The cumulative N₂O emissions of natural wetlands,rice-wheat rotation fields,and greenhouse vegetable fields during the entire observation period were 3.35 kg N ha^-1,14.38 kg N ha^-1,and 81.62 kg N ha^-1,respectively.N₂O emissions from natural wetlands are sluggish,with emissions concentrated in spring and summer.The N₂O emission of rice-wheat rotation fields is mainly concentrated in the wheat season,and the N₂O emission in the rice season is relatively low.N₂O emissions of greenhouse vegetable fields are mainly concentrated in the summer leisure period.The order of the comprehensive greenhouse effect of CH₄and N₂O under different land use types was:rice-wheat rotation field(26704.16 kg eq-CO₂ha^-1)>natural wetland(25266.30kg eq-CO₂ha^-1)>greenhouse vegetable field(22543.51 kg eq-CO₂ha^-1).The three did not show significant differences.CH₄is the dominant greenhouse gas in natural wetlands,and its contribution to the greenhouse effect reaches 96.04%.CH₄is also the dominant greenhouse gas in rice-wheat rotation fields,and its contribution to the greenhouse effect reaches 83.95%.N₂O is the dominant greenhouse gas in greenhouse vegetable fields.The CH₄ absorbed by the soil partially offsets the greenhouse effect produced by N₂O.The offset is about 7.32%of the warming potential caused by N₂O during the entire observation period.The transformation of land use types significantly changed the physical and chemical properties of soil.The results of multiple linear regression analysis showed that the soil factors driving CH₄ emission from rice-wheat rotation fields were soil electrical conductivity and nitrate nitrogen content,and the soil factor driving N₂O emission from rice-wheat rotation fields was soil ammonia nitrogen content.The soil factors that drive N₂O emissions from greenhouse vegetable fields were soil water content and p H.In summary,the transformation of typical natural wetlands in the Taihu Lake region into rice-wheat rotation fields has enhanced the comprehensive greenhouse effect of CH₄ and N₂O;the transformation of rice-wheat rotation fields into greenhouse vegetable fields has weakened the comprehensive greenhouse effect of CH₄ and N₂O.When evaluating the environmental effects caused by the transformation of land use,attention should be paid to the greenhouse gas emission characteristics of different ecosystems.Also,effective carbon and nitrogen fixation and emission reduction measures should be taken in time to alleviate the greenhouse gas emissions caused by the transformation of land use.