秦岭火地塘林区不同海拔不同林型土壤CO_2、CH_4、N_2O通量研究

二氧化碳(CO_2)、甲烷(CH_4)、氧化亚氮(N_2O)是3种主要的温室气体,温带森林土壤是CO_2、N_2O重要的源,是CH_4重要的汇,以前的研究大部分都关注这3种温室气体在时间上的变化,而很少开展在空间变化上的研究。2014年10月至2015年10月,采用静态箱-气相色谱法对秦岭南坡火地塘林区不同海拔(海拔1 560、1 585、1 963、2 040、2 160m,分别为落叶阔叶林、温性针叶林、温性针叶林、寒温性针叶林、落叶阔叶林)森林土壤CO_2、CH_4和N_2O通量进行了为期1a的监测。结果表明,CO_2全年都为排放,季节波动较大,总体上随海拔增加排放量减少,海拔由低到高(包括3种林型)年排放量依次为:19.12、12.53、11.78、16.95、14.87t·hm^-2;CH_4全年主要为吸收,在非生长季出现排放,季节波动幅度较大,总体上随海拔增加吸收量增加,海拔由低到高年通量依次为:-2.57、-3.60、-5.94、-5.59、-3.92kg·hm^-2;N_2O全年以排放过程为主,存在吸收现象,季节波动幅度不大,海拔对其通量影响不明显,海拔由低到高年排放量依次为:0.23、0.62、0.63、0.60、0.95kg·hm^-2。土壤温度是影响CO_2、N_2O通量的关键因子。5个样地森林土壤CO_2通量与土壤铵态氮含量(20～40cm)显著相关(P<0.05)。高的土壤NH_4^+含量对CH_4的吸收有抑制作用。在冻融交替期,降雨对N_2O的通量有明显影响。海拔由低到高5个样地的GWP(全球增温潜势)分别为:119.13、12.65、11.85、17.02t·hm^-2和15.07t·hm^-2。

Soil-Atmosphere Exchange of Nitrous Oxide,Methane and Carbon Dioxide of Different Forest Types at Different Elevations in Huoditang Forest Region of Qinling Mountains

Carbon dioxide (CO2),methane (CH4) and nitrous oxide (N2O) are the three main greenhouse gases that have large impacts on the global warming.Temperate forest soils are considered as major sources of CO2 and N2O,and also are important sinks for CH4.Although there are increasing number of studies on greenhouse gas fluxes between forest soils and the atmosphere,the majority of these studies focus on the temporal variations of these trace gases.The spatial patterns of these trace gases are still highly uncertain.From October 2014 to October 2015,static chamber and gas chromatography techniques were used to monitor CO2,CH4 and N2O fluxes of the forest soils at 5 elevation sites (1560,1585,1963,2040,and 2160m,the corresponding forest types including deciduous broad-leaved,temperate coniferous,temperate coniferous,cold temperate coniferous and deciduous broad-leaved forests) in Huoditang Forest Region on the southern slope of the Qinling Mountains.The results showed that CO2 emitted from the five elevation sites throughout the year.The seasonal CO2 emissions varied widely.Generally,the annual cumulative CO2 emissions decreased with the increase of the elevation.The annual cumulative CO2 from low to high elevation sites (including three forest types) were as follows:19.12,12.53,11.78,16.95 and 14.87 t·hm^-2.At most of the sampling times,CH4 consumptions were monitored.However,several times of CH4 emissions were also found.The seasonal CH4 fluxes varied widely.In general,the annual cumulative CH4 consumption increased with the increase of the elevation.The annual cumulative CH4 consumption from low to high elevation sites were as follows:-2.57,-3.60,-5.94,-5.59 and -3.92 kg·hm^-2.At the five elevation sites,N2O emitted throughout the year.However,several times of N2O consumption were also detected.The annual cumulative N2O from low to high elevation sites were as follows:0.23,0.62,0.63,0.60,0.95 kg·hm^-2.Soil temperature was identified as the key factor determining the temporal variability of CO2 and N2O fluxes.There was significant correlation between CO2 flux and soil ammonium content (20-40cm)(P<0.05) at all the five elevation sites.The high soil nitrate content had an inhibiting effect on CH4 consumptions.During freezing and thawing period,rainfall had significant impact on the flux of N2O.From low to high elevations,the global warming potential (GWP) of the five sites were as follows:119.13,12.65,11.85,17.02 and 15.07 t·hm^-2.