Research On The Characteristics Of Greenhouse Gas Emission From Urban Garden Grassland Soil In Beijing

With the rapid development of urbanization and the improvement of greening level,the soil area of urban grassland has increased rapidly in recent years,which will inevitably affect the concentration of greenhouse gases in the city.However,there were few reports on the related emission fluxes and estimation models.This study was conducted during the 2018 growing season,with the cold-season type?Mixed grass of Tall fescue and Bluegrass?,warm-season?Buffalo grass?,undergrowth?Carex giraldiana?and their soils were studied.The static black box-gas chromatography based observation technique was used to conduct the field in situ emission fluxes of CO₂,CH₄,N₂O and NO and their key influencing factors.The high frequency observation analysis the seasonal variation of greenhouse gas emission fluxes in grasslands and their soils,and established an estimation model for greenhouse gas emission fluxes in Beijing urban grassland,finally,the difference and influence mechanism of greenhouse gas emission fluxes of different grasslands and their soils were further discussed,so as to provide important guidance for reasonably reducing greenhouse gas emission of urban grassland.The main conclusions are as follows:?1?The CO₂ emission fluxes of different grasslands,grass of undergrowth and their soils were positive in both summer and autumn,and they were all sources of atmospheric CO₂emissions,showing the characteristics of“summer high and low autumn”.The average CO₂emission fluxes of mixed grass,buffalo grass,and carex giraldiana were:361.29 mg·m^-2·h^-1,302.02 mg·m^-2·h^-1,290.67 mg·m^-2·h^-1,the average CO₂ emission fluxes of their soils were:270.30 mg·m^-2·h^-1,263.66 mg·m^-2·h^-1,241.72 mg·m^-2·h^-1.?2?The CH₄ fluxes of different grasslands,grass of undergrowth and their soils were alternately released and absorbed in summer and autumn.,but the overall performance were the weak absorption of atmospheric CH₄.The average CH₄ emission fluxes of mixed grass,buffalo grass and carex giraldiana were:-30.82?g·m^-2·h^-1,-13.08?g·m^-2·h^-1,-35.49?g·m^-2·h^-1,the average CH₄ emission fluxes of their soils were:-50.52?g·m^-2·h^-1,-41.02?g·m^-2·h^-1,-16.39?g·m^-2·h^-1.?3?The N₂O emission fluxes of different grasslands,grass of undergrowth and their soils were positive in both summer and autumn,and they were all sources of atmospheric N₂O emissions,showing the characteristics of“summer high and low autumn”.The average N₂O emission fluxes of mixed grass,buffalo grass,and carex giraldiana were:26.60?g·m^-2·h^-1,59.87?g·m^-2·h^-1,21.63?g·m^-2·h^-1,the average N₂O emission fluxes of their soils were:20.47?g·m^-2·h^-1,47.02?g·m^-2·h^-1,23.00?g·m^-2·h^-1.?4?The NO emission fluxes of different grasslands,grass of undergrowth and their soils were positive in both summer and autumn,and they were all sources of atmospheric NO emissions,showing the characteristics of“summer high and low autumn”.The average NO emission fluxes of mixed grass,buffalo grass,and carex giraldiana were:22.68?g·m^-2·h^-1,48.49?g·m^-2·h^-1,23.43?g·m^-2·h^-1,the average NO emission fluxes of their soils were:19.66?g·m^-2·h^-1,38.26?g·m^-2·h^-1,17.37?g·m^-2·h^-1.?5?The seasonal variation of CO₂,CH₄,N₂O and NO emission fluxes of different grasslands,grass of undergrowth and their soils were mainly affected by temperature and soil moisture.The CO₂,N₂O,NO emission fluxes reached a significant level between temperature,soil temperature and humidity?5 cm,10 cm?,which were suitable for fitting with exponential equation or linear equation;CH₄ emission fluxes and temperature,soil temperature?5 cm,10 cm?reached a significant level of 0.05.The mixed grassland and its soil,the carex giraldiana and its soil and soil moisture reached a significant level of 0.05,which were suitable for fitting with the GaussAmp or linear equation.?6?The warming potential of different grasslands,grass of undergrowth and their soils had the following rules:mixed grassland>buffalo grassland>carex giraldiana>buffalo grassland soil>mixed grassland soil>carex giraldiana soil,the warming potential of mixed grassland increased by 12.36%and 23.75%compared with buffalo grassland and carex giraldiana,the buffalo grassland increased by 10.14%compared with the carex giraldiana.According to the comprehensive analysis,the cold-season grassland?mixed grass of tall fescue and bluegrass?had the strongest warming potential,following by the warm-season grassland?buffalo grassland?,carex giraldiana was the weakest.