Diurnal Variation Characteristics And Influencing Factors Of Soil CO₂ And CH₄ Fluxes Pinus Tabulaeformis Artificial Forest Of Daqing Mountain Inner Mongolia

In this study,static chamber-gas chromatography was used to observe the soil CO₂and CH₄fluxes of Pinus tabulaeformis forest in Daqingshan area.The diurnal variation characteristics of soil greenhouse gas fluxes were studied,and the representative sampling periods of each month were determined.The soil temperature,soil moisture,atmospheric temperature and humidity and their correlation with greenhouse gas fluxes were analyzed,and the cumulative fluxes of soil CO₂and CH₄were estimated.The results are as follows:1.The soil CO₂flux showed a‘single peak’change.Consistent with the trend of soil temperature,the peak appeared at 11:00～13:00,and the minimum appeared at 4:00～5:00.The diurnal variation was the largest in August and the smallest in June.The soil CH₄flux showed a‘bimodal’or‘multimodal’trend.The peak appeared at 11:00～15:00,and the minimum appeared at7:00～9:00.The absolute value of soil CH₄absorption flux was August>July>June>September.The soil CO₂flux in the growing season was selected at 9:00 and 17:00～19:00 to observe the soil respiration.Soil CO₂flux was measured at 9:00 and 17:00～19:00,while soil CH₄flux was measured at9:00 and 19:00.2.The change of soil CO₂flux during the freezing period showed a‘bimodal’change,and the ablation period showed a‘unimodal’change.The change of soil CH₄flux during freeze-thaw period showed a‘bimodal’change.The absorption peak was reached at 10:00,and the minimum value appeared at 8:00.During the freezing and thawing period,the sampling time of CO₂and CH₄fluxes was around 9:00 and 13:00.3.There was a significant exponential relationship between soil CO₂flux and atmospheric temperature,soil temperature in 0～5 cm and 5～10 cm soil layers,and a significant negative correlation with humidity.There was no significant negative correlation between soil CH₄flux and soil temperature and soil moisture in growing season.During the freeze-thaw period,soil CO₂flux was significantly positively correlated with soil temperature in 5～10 and10～20 cm soil layers,and significantly negatively correlated with soil moisture in 0～5,5～10 and 10～20 cm soil layers.During the freeze-thaw period,there was no significant correlation between soil CH₄flux and soil temperature,but there was a significant negative correlation between soil CH₄flux and soil moisture in 0～5 and 5～10 cm soil layers.4.During the observation period of 2020.05～2021.04,the annual cumulative fluxes of soil CO₂and CH₄were about 13287.1 kg·hm^-2and-3.6kg·hm^-2,respectively.The cumulative fluxes of soil CO₂and CH₄in the growing season accounted for 89.3%and 48.6%of the annual fluxes,respectively.The cumulative fluxes of soil CO₂and CH₄in the freeze-thaw period accounted for 5.9%and 21.9%of the annual fluxes,respectively.