| In order to study the effects of understory vegetation and litter on the soil greenhouse gas fluxes of natural forests in the cold temperate zone of China,emissions of CO2,CH4,and N2O under four treatments(natural state,removal of litter,removal of understory vegetation,and removal of understory vegetation and litter)were continuously measured by using the static chamber-gas chromatography method,in four forest soil ecosystems(Betula platyphylla,Populus davidiana,Pinus sylvestris var.mongolica and Larix gmelinii)of the cold temperate zone China(north of Daxing'an Mountains)from May to September 2019.The study of greenhouse gas emission characteristics of different forest types in the cold temperate zone of China will provide a theoretical basis for the study of the impact on the regional ecological environment.Research indicated:(1)The soils under the natural state of the four forest types behaved as the "source" of CO2 and N2O,and the "sink" of CH4.The average soil CO2 flux of the four forest types followed the order of Pinus sylvestris var.mongolica forest(398.26±79.60)mg/(m2·h)>Populus davidiana forest(364.18±74.78)mg/(m2·h)>Betula platyphylla forest(335.63±33.81)mg/(m2·h)>Larix gmelinii forest(315.36±70.64)mg/(m2·h),and the average soil CO2 flux of Pinus sylvestris var.mongolica forest was significantly higher than those of other three forest types(P<0.05).The average absorption flux of CH4 in the four forest types shows that Betula platphylla forest(-79.23±14.92)?g/(m2·h)>Populus davidiana forest(-64.27±9.60)?g/(m2·h)>Pinus sylvestris var.mongolica forest(-62.54±15.48)?g/(m2·h)>Larix forest(-48.73±12.26)?g/(m2·h),the average absorption flux of CH4 in the soil of Larix gmelinii forest was significantly lower than the other three forest types(P<0.05).The average soil N2O flux of the four forest types were as follows:Populus davidiana forest(20.26±4.68)?g/(m2·h)>Betula platyphylla forest(19.61±5.05)?g/(m2·h)>Pinus sylvestris var.mongolica forest(18.65±3.90)?g/(m2·h)>Larix gmelinii forest(17.44±5.10)?g/(m2·h),and the average flux of soil N2O in Populus davidiana forest was significantly higher than that in the Larix gmelinii forest(P<0.05).In general,Larix gmelinii forest had the lowest absorption of greenhouse gases and the lowest emissions.(2)The removal of litter would increase the soil CO2 emissions of broad-leaved forests by 0.96%?8.49%,and reduced the soil CO2 emissions of coniferous forests by 7.44%?10.35%,while the difference was not significant(P>0.05).After removing the understory vegetation,the soil CO2 flux of Pinus sylvestris var.mongolica forest remained basically unchanged,while the average soil CO2 flux of Betula platyphylla forest,Populus davidiana forest and Larix gmelinii forest increased significantly by 27.57%,15.84%and 24.13%(P<0.05).Under the removal of understory vegetation and litter,the average soil CO2 flux of Betula platyphylla forest,Populus davidiana forest and Larix gmelinii forest increased significantly by 20.05%?25.34%(P<0.05),the average value of soil CO2 fluxes in Pinus sylvestris var.mongolica forest decreased by 12.36%(P<0.05).It can be seen that partial or complete removal of understory vegetation and litter reduced soil CO2 emissions of Pinus sylvestris var.mongolica forest,while increased soil CO2 emissions of Betula platyphylla forest and Populus davidiana forest.Larix gmelinii forest was different under different understory management methods.(3)During the whole study period,the soil CH4 fluxes of the four forest types were all negative values,which represented the absorption of CH4.In the four forest types,soil CH4 absorption flux under litter removal increased by 2.12%?12.15%(P>0.05)compared with the natural state.After removing the understory vegetation,the soil CH4 absorption flux of the four forest types increased by 0.84%?20.55%,while it was only signficant on Populus davidiana forest(P<0.05).After removing the understory vegetation and litter at the same time,there was no significant effect on the CH4 flux of Betula platyphylla forest and Pinus sylvestris var.mongolica forest(P>0.05),while the impact on Populus davidiana forest and Larix gmelinii forest was significant(P<0.05).In general,the removal of litter,understory vegetation,and both removals,will increase the absorption of CH4 by the four forest types of soil.(4)The four forest types soils were the "sources" of N2O flux,and they showed different trends.After removing litter,the reduction of soil N2O flux ranged from 5.42%to 13.01%,and the change under Larix gmelinii forest was significant(P<0.05).After removing the understory vegetation,the soil N2O flux of the four forest types increased in varying degrees,with an increase of 2.32%?10.64%(P>0.05).After both removals,the soil N2O flux in the Betula platyphylla forest,Populus davidiana forest and Pinus sylvestris var.mongolica forest increased by 2.77%,7.36%and 2.34%respectively(P>0.05),but Larix gmelinii forest decreased by 8.61%(P>0.05).In general,the removal of litter will reduce the soil N2O flux,and the removal of understory vegetation will increase the soil N2O flux.For both removals,only Larix gmelinii forest showed a decreasing trend of N2O.(5)The correlation between soil CO2,CH4,and N2O fluxes and soil temperature was better than that of soil moisture,which showed that the influence of soil temperature on soil greenhouse gas fluxes was more obvious in this region.The emission or absorption of soil greenhouse gases was closely related to soil temperature in this region.Our results showed that the influence of soil temperature on soil CO2 flux was greater than the other two greenhouse gases.Thesoil moisture had little effect on the fluxes of the three greenhouse gases.(6)Based on the 100-year scale,the global warming potential(GWP)of the four forest types under different treatments showed that Betula platyphylla forest and Populus davidiana forest had the lowest warming potential under natural conditions,and Pinus sylvestris var.mongolica forest was the lowest under both removal,Larix gmelinii forest was the lowest under the removal of litter,but the best choice was the natural state.Therefore,the broad-leaved forest and Larix gmelinii forest should maintain the original ecology of the understory as far as possible,and the forest bed of Pinus sylvestris var.mongolica forest should be cleaned accordingly.However,from the perspective of forest types,Larix gmelinii,as the top community in this region,had the lowest warming potential in its natural state. |
PDF Full Text Request