| Carbon dioxide(CO2)is an important source of greenhouse gases leading to global climate change and has an important impact on atmospheric greenhouse gas concentration.Artificial forest is an important component of forest ecosystem.Chinese fir plantations account for 30%of the total area of China’s plantations.Forest age may be an important factor affecting soil CO2 flux,so it is of great theoretical and practical significance to study soil CO2 flux and its influencing factors in Chinese fir plantations of different forest ages for the evaluation of carbon sink function and scientific management of plantations.In order to explore the characteristics and influencing factors of surface carbon dioxide flux changing with age of Chinese fir plantation,this paper took 10 Chinese fir plantations in Huitong,Hunan province,as the research object.The use of static box-gas chromatography for soil CO2 flux for one-year field positioning observation,while recording the forest temperature,surface temperature,soil underground 5cm temperature,collect soil samples to determine soil physical and chemical properties(soil moisture content,WFPS,pH,Eh,DOC and SOC).It is of great theoretical and practical significance to analyze the influence of environmental factors on soil carbon dioxide flux of Chinese fir plantations of different ages.The main results are as follows:(1)There was no obvious change trend among stand age,forest temperature,surface temperature,soil 5 cm temperature and soil 5 cm humidity,and this change varied between months and seasons.The variation trends of in-forest temperature,surface temperature and soil 5 cm temperature in different forest-age fir plantations were basically the same at monthly and seasonally,and the relationship among the three kinds of temperature was the forest temperature>soil 5 cm temperature>surface temperature.(2)Soil physical and chemical properties of Cunninghamia lanceolata plantation varied according to stand age.With the increase of stand age,soil moisture content had no obvious trend of change,and the fluctuation among stand ages was small(less than 5.3%).With the increase of stand age,WFPS showed a decreasing,increasing,decreasing and increasing trend,and fluctuated greatly among stand ages(more than 14%).With the increase of stand age,pH showed a decreasing-increasing trend,and the variation range was basically the same between stand ages(about 0.4).The changes of forest age and Eh were different in different months.The variation range of 6a Eh was the largest(133.25 mV),while that of 86a was the smallest(31.87 mV).With the increase of stand age,DOC showed an uptrend and down trend,with the smallest variation in DOC in August(88.23 mg/kg)and the largest in March(152.04 mg/kg).The variation range of 86a DOC was the smallest(277.69 mg/kg),14a DOC the largest(454.72 mg/kg),32a DOC the second(430.97 mg/kg).The change of forest age and SOC were different in different months.The fluctuation of SOC was the lowest in August(5.10 g/kg)and the highest in March(13.15 g/kg).The range of 6a SOC was the smallest(8.43 g/kg),followed by 24a(8.74 g/kg),35a maximum(17.15 g/kg).(3)Soil CO2 flux changed according to forest age,and there were differences between forest age and soil CO2 flux at monthly and seasonally,and the seasonal variation was significant.With the increase of stand age,annual soil CO2 flux,total soil CO2 emission all showed a decreasing-increasing trend.The variation range of soil CO2 flux between stand ages was the lowest in November(74.95 mg/m2h)and the highest in August(482.58 mg/m2h).During the observation period,soil CO2 flux at 6a(767.06 mg/m2h),14a(730.84 mg/m2h)and 35a(737.36 mg/m2h)fluctuated significantly(more than 730 mg/m2h).32a(407.94 mg/m2h)had the lowest fluctuation.The seasonal variation of soil CO2 flux showed as follows:winter<spring<autumn<summer,with the maximum variation in summer(337.66 mg/m2h)and the minimum in winter(64.73 mg/m2h).Soil CO2 flux ranged from 232.35±121.01 to 363.02±209.08 mg/m2h,with the minimum at 29a and the maximum at 6a.The annual flux of soil CO2 ranged from 17.20 t/hm2yr to 25.49 t/hm2yr in cunninghamia lanceolata plantations of different ages,with the minimum at 32a and the maximum at 6a,and the range was 8.29 t/hm2yr.(4)In cunninghamia lanceolata plantation,the effects of environmental factors on soil CO2 flux varied with stand age,and temperature,soil Eh and DOC were the main factors affecting soil CO2 flux.The temperature sensitivity(Q10)of soil CO2 flux at different forest ages ranged from 1.04 to 2.10,with the minimum at 24a and the maximum at 19a.The influencing factors of soil CO2 flux in 6a were temperature(p<0.01),Eh(p<0.01),DOC(p<0.01)and SOC(p<0.05).The influencing factors of 11a were temperature(p<0.01),Eh(p<0.05)and DOC(p<0.05).The influencing factors of 14a were temperature(p<0.01),Eh(p<0.05)and DOC(p<0.01).The influencing factors of 19a were temperature(p<0.01),pH(p<0.01),soil moisture content(p<0.05),DOC(p<0.01)and SOC(p<0.01).The influencing factors of 24a were temperature(p<0.01),Eh(p<0.01)and DOC(p<0.05).The influencing factors of 29a were temperature(p<0.01),DOC(p<0.01),The influencing factors of 32a were temperature(p<0.01),Eh(p<0.01)and DOC(p<0.01).The influencing factors of 35a were temperature(p<0.01),pH(p<0.05),Eh(p<0.01),soil moisture content(p<0.05),DOC(p<0.01)and SOC(p<0.01).In conclusion,the seasonal and annual changes of soil CO2 flux in Chinese fir plantation decreased first and then increased with the increase of stand age,and the influencing factors of soil CO2 flux in different stand ages were different. |
