| The forest soil,which is the biggest carbon pool of land ecological systems,can regulate the concentration of CO2,N2O and CH4 in the atmosphere.To explore the effects of forest harvest on soil carbon storage and greenhouse gas flux,by using the static closed chamber-gas chromatograph technique and IRGA methods,the fluxes of soil CO2,CH4 and N2O and soil carbon storage were measured in the secondary forest with different harvest methods(partial cut 1(50%of the stand volume removed),partial cut II(25%of the stand volume removed),afforestation(forestation after clear cutting),cropland(farming after clear cutting),and control(uncut)).To understand the long effect of harvest on the fluxes of greenhouse gases,the fluxes of soil CO2,CH4 and N2O were also measured from the secondary forest and the adjacent larch plantation.The results show that:1)At the 3 years after harvesting,the rates of soil CO2 emissions rates increased in the secondary forest,highest soil CO2 emissions were measured in the plots of afforestation,32%higher than control,and 20%higher in the partial cut plots.But at the 9th year after harvesting,the rates of soil CO2 emissions rates decreased in the plot of afforestation,while that increased in the plots of partial cut I and cropland.The rates of soil CH4 uptake decreased after harvesting.Soil can uptake lower CH4 in the plots of clear cut and partial cut II.Soil could absorb more CH4 in the plots of control and partial cut I.After cutting,soil N2O emission rates increased,the highest in the plots of clear cut,higher in the plots of partial cut,and lowest in the control.Soil CO2 emission and CH4 uptake mainly concentrated in the growing season,and the variations of soil N2O emission flux were lower in growing season and dormant season.2)After harvesting,soil temperature,soil moisture,soil NO3--N content,soil microbial biomass nitrogen,net nitrogen mineralization rate and net nitration rate also increased.Soil CO2 emissions rate correlated with soil temperature and soil water content.the soil CO2 emissions could be affected by soil temperature in the plots of clear cut,and be influenced by soil moisture in the plots of control and partial cut II.Soil CH4 uptake rates are positively related with soil temperature,but correlated with soil moisture negatively.Soils N2O emissions rate were related with soil temperature,soil and soil NO3--N content positively.After harvesting,the variation of the fluxes of soil CO2,N2O and CH4 may be related with harvest residue,so soil NO3--N content.3)After conversion secondary forest to larch plantation,soil CO2 emission rates declined,soil CH4 absorption and N2O emission rate increased.Soil temperature,soil moisture,soil NO3--N content in the secondary forest were higher than that in the larch plantation.Soil CO2 emission and soil CH4 absorption were influenced by soil temperature and soil water content,while soil N2O emissions were related with soil temperature.Higher soil CO2 emission rate in the secondary forest may be related with higher soil temperature and soil water content.Canopy and litter could intercept more rainfall in the larch plantation,and decreased soil water content.It resulted that soil consumed more CH4 in the larch plantation.While,more soil N2O emission in the larch plantation may be related to thicker litter,which can intercept more rainfall.4)Soil organic carbon content,total nitrogen content and C/N had little difference after harvesting in the secondary forest.Soil organic carbon content and total nitrogen content were higher in the lower depth,Soil organic carbon contents in the depth of 0-10 cm were 15 to 20 times higher than that in the depth of 50-70cm.soil layer soil carbon content for the bottom of the soil,and soil nitrogen content were 10 times higher.5)At the 3 years after harvesting,soil carbon density ranged from 11.5 to 13.7 kg m-2 in the secondary forest.Soil carbon storage increased with time,the largest increase were in the clear cut,the higher in the partial cut,the minimum in the control.Soil carbon density reduced gradually with the depth.Soil in the depth of 0-30cm could storage 80%carbon.But at the 9th year after harvesting,soil carbon density decreased in all plots.Then all data revised given fixed uncut,soil carbon density increased in the harvesting plots.The increase of soil carbon storage was originated from more harvest residue in the plots of harvest.Overall,lower cutting strength can alleviate greenhouse gas emission flux in the secondary forest.At the 9TH yeat,soil CO2 emission decreased in the plots of afforestation.Greenhouse gas fluxes changed after conversion secondary to larch plantation,which may be related with tree species.It suggested that the effect of harvest on greenhouse gas fluxes may be short period.More harvest residue in the plots of harvest could increase soil carbon storage. |
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