| The understanding of diurnal variation of soil greenhouse gas emission fluxes will help to reduce the uncertainty of the carbon estimation of terrestrial ecosystem.However,the influence of thinning on diurnal emission variation of greenhouse gas is still unclear.The diurnal fluxes of CO2,CH4 and N2O and their relationship with environmental factors(temperature,humidity)from Larix gmelinii plantations under different thinning intensities(contrast,LW;mild thinning,LQ-25%and severe thinning,LZ-50%,the thinning had been 21 years.)were measured by the static chamber method in temperate Maoershan Mountains in northeastern China,to reveal the effects of thinning on diurnal variation of soil greenhouse gas emission fluxes and main factors.And the optimal observation duration for CO2,N2O and CH4 fluxes were investigated under the different thinning intensities in spring,summer and autumn,to provide a scientific basis for enhancing the representativeness of observation results in a long time scale study.The results showed that:(1)The effects of thinning on the air temperature and soil temperature and humidity were different in different seasons.LZ increased the average daily temperature of soil 3 0-40cm in spring by 42.6%-81.1%(p<0.05),but had no significant effect on summer and autumn temperature.Moreover,LQ and LZ increased the average daily moisture content of soil 0-40cm(43.9%-73.2%,p<0.05),while there was no significant effect on spring and summer.(2)The effects of thinning on the soil CO2 diurnal emission(180.97-380.55mg.m-2.h-1)were different among spring,summer and autumn.LQ and LZ reduced the CO2 diurnal emission by 22.8?29.8%(LZ,p<0.05)in autumn,but there was no significant effect on it in spring and summer.The patterns(day?night,day?night and day>night)and trends(unimodal type,constant type and skewness)of CO2 diurnal variation were different in different seasons.The pattern and trend were not changed by thinning.(3)The effects of thinning on the soil CH4 diurnal emission(-0.021--0.076 mg.m-2.h-1)were different in different seasons.LQ and LZ reduced the CH4 diurnal emission by 26.2%-27.6%(p>0.05)or 38.2%-50.0%(p<0.05)in spring and autumn,but there was no significant effect on it in summer.The patterns(night>day,day?night and day?night)and trends(skewness,ladder and constant type)of CH4 diurnal variation were also different in different seasons.The patterns and trends were changed by thinning in spring and summer(4)The soil N2O diurnal emission(0.004-0.053mg.m-2.h-1)were not significantly affected by thinning in different seasons,but LQ reduced the amount of N2O diurnal emission by 21.6%?55.6%(p>0.05)in summer and autumn.The patterns(day?night,day?night and day>night)and trends(constant type,constant type and unimodal type)of N2O diurnal variation were different in different seasons.The pattern and trend were changed by LZ in summer,and the trends were changed by LQ and LZ in autumn.(5)The correlation between soil C02 diurnal fluxes and soil temperature was increased,but the correlation between it and soil moisture was reduced by thinning in spring and autumn.The correlation between soil CH4 diurnal fluxes and soil temperature and humidity were reduced by thinning in spring,and LZ increased the correlation between it and deep soil temperature and humidity in summer.The correlation between N2O diurnal emission and soil moisture was reduced in spring and autumn,but the correlation between it and soil temperature and humidity were increased in summer by thinning.(6)In Larch plantation in temperate Maoershan of China,the optimal observation time of 3 treatments of CO2 flux was unified to 9:00 or 21:00 in spring,6:00 or 12:00 in summer and 21:00 in autumn.The best observation time of CH4 flux was 12:00 in spring;LW and LQ were 9:00 and LZ was 12:00 in summer;LW and LQ were 9:00 and LZ was 15:00 in autumn.In spring N2O flux,LW was 12:00.LQ and LZ were 9:00.In summer,all three were 15:00;In autumn,LW and LZ were 12:00.LQ was 15:00. |
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