Variation And Coupling Of Soil CO₂,CH₄ And N₂O Fluxes In A Robinia Pseudoacacia Plantation In The South Of The Taihang Mountains

In this study,soil CO2,CH4 and N2O fluxes of the 50-year-old Robinia pseudoacacia plantation was being measured in situ for a year(2017.09-2018.08)by using chamber-laser method in the south of the Taihang Mountains.The study revealed the daily and monthly dynamics of soil CO2,CH4 and N2O fluxes,determined the monthly representative measurement time period of soil CO2,CH4 and N2O fluxes.Meanwhile,the temperature and humidity factors of each soil layer were observed to analyze the response of soil CO2,CH4 and N2O fluxes to them.In addition,the coupling between the three greenhouse gases was discussed,and the cumulative flux and warming potential of soil greenhouse gases in the region were evaluated to provide data support and theoretical basis for Chinese forestry to cope with global warming.During the observation period,the soil of Robinia pseudoacacia plantation in the south of the Taihang Mountains was the source of CO2 and N2O,the sink of CH4.The diurnal variation of soil CO2,CH4 and N2O flux were generally characterized by "nocturnal large and diurnal small".CO2 flux had obvious seasonal characteristics(high in summer,low in winter),while the seasonal changes of CH4 and N2O were not obvious.The monthly representative measurement time period of soil CO2,CH4 and N2O flux were different.Therefore,fluxes in a specific month need to be measured in a specific time period.During the observation period,The natural logarithmic CO2 and N2O fluxes showed extremely significant linear correlation with the temperature of each soil layer(5?15?25 and 35cm)(p<0.01),and soil CH4 flux has an extremely significant quadratic function relationship with the temperature of each soil layer(p<0.01).Shallow(5 and 15cm)soil temperature had the higher explanatory rate for greenhouse gas changes.There was a significant correlation between the three soil greenhouse gases and the water content in a specific soil layer,but the explanatory rate of soil moisture on the change of the three greenhouse gases was small(the correlation coefficient was small).Soil CO2 flux had a negative coupling with soil CH4 flux,and it had a positive coupling with soil N2O flux.Soil CH4 flux had a negative coupling with soil N2O flux.The annual cumulative CO2 flux of the Robinia pseudoacacia plantation in the south of the Taihang Mountains was 37478.75 kg·hm-2.The magnitudes of the cumulative CO2 flux in spring,summer,autumn and winter were 11850.4,15783.4,8263.5 and 1581.3 kg·hm-2,respectively.The cumulative CO2 flux in the whole growing season(spring and summer)accounted for up to 73.8%of-the annual total.In this site,the cumulative soil CH4 and N2O fluxes in 12,1,3,4,5,6,7 and 8 months were-2.0,-2.1,-0.15,-0.22,-0.27,-0.12,-0.16,-0.14 kg·hm-2 and 0.046,0.044,0.031,0.358,0.452,-0.0.017,-0.0.028,0.208 kg·hm-2,respectively.During the growing season(March to August),the cumulative soil CH4 and N2O fluxes were 1.06 and 1.004 kg hm-2,respectively,while the relative greenhouse potentials of CH4 and N2O were-54.99 and 486.73 kg CO2·hm-2,respectively.