The Characteristics And Influencing Factors Of Carbon Fluxes In Coniferous And Broad-leaved Mixed Forests In Jinyun Mountain

The study of the carbon cycle of terrestrial ecosystems is one of the main research contents of the global carbon cycle in the context of climate change.Forest ecosystems,as the largest carbon pool in terrestrial ecosystems,are of great significance in maintaining the balance of carbon and oxygen in the biosphere.In this study,the carbon fluxes of subtropical coniferous and broad-leaved mixed forests in Jinyun Mountain in Chongqing were measured by using the eddy covariance method.Carbon flux data and corresponding weather data for a period of one year from June 2016 to May 2017 were obtained.These data were then used to analyze the dynamic changes in carbon flux over the day,month,season,and year.The carbon flux situation during this period and its response to environmental factors(including light,temperature,humidity,etc.)were clarified to further explain the regulation mechanism of the dynamic changes of carbon flux in forest ecosystems.After studying the carbon fluxes and environmental factors in the coniferous and broad-leaved mixed forest ecosystem in Jinyun Mountain,the following results were obtained:(1)The average daily CO2 fluxes of the coniferous and broad-leaved mixed forest ecosystem in Chongqing's Jinyun Mountain were "U“shaped during the month and quarter,and negative during the day.Fixed carbon was positive at night.The peak value of the daily average carbon sink of released carbon appeared in July and the minimum value appeared in December.In the summer,the carbon sink had the longest time and the largest amount of fixed carbon on the day,followed by spring and autumn,with the shortest carbon sink time and the smallest daily carbon fixation in winter.(2)The total amount of NEE,Re,and GEE in the study period was-566.49,1196.68,and-1761.63 gC·m-2,respectively,and the cumulative value of each month was the largest in summer,closely followed by spring/autumn,and smallest in winter.Excluding carbon sources in December,all other months showed carbon sinks.The monthly minimum of NEE accumulated in July was-129.53 gC·m-2,and the maximum was in December,which was 20.38 gC·m-2.(3)Daytime CO2 flux is mainly affected by photosynthetically active radiation PAR,and the relationship between the two is in accordance with the Michaelis-Menten model.Saturated vapor pressure deficit VPD and temperature Ta are the secondary influence factors of daytime CO2 flux.When VPD increases to more than 1kPa,the response of CO2 to PAR will be weakened;when Ta?25?,the CO2 flux will be inhibited.The dominant factor of nighttime CO2 flux is soil temperature Ts and the relationship between the two is in line with Van't Hoff model.Soil volumetric water content SWC has a certain effect on nighttime CO2 flux.The optimum SWC is 0.28m-3·m-3.It will have an inhibitory effect on nighttime CO2 flux to a certain extent,but its function in this study is small.(4)The meteorological factors such as temperature Ta,soil temperature Ts,air saturation deficit VPD and soil water content SWC have a significant effect on the monthly accumulation of Re and GEE.GEE and Re have an obvious linear correlation with Ta Ts and VPD;Re associated with these SWC a quadratic curve;GEE is associated with PAR for linear fitting.NEE to Ta,Ts,VPD,SWC,PAR are related in response to a quadratic curve,that's the outcome of combined action of photosynthesis and respiration.