| Under the background of global change,the problems caused by climate warming has been brought to the attention of the many fields,CO2,CH4 and N2O are the three main gases that cause the greenhouse effect is being widely attention.At present,a lot of fossil fuel combustion,vehicle emissions,industrial waste gas are acknowledged as the main reason for greenhouse gas emissions,and the greenhouse gases emitted by the ecosystem itself is one of the important sources of greenhouse gases.Forest ecological system as an important part of terrestrial ecosystem,which gases plays a vital role in the emissions of greenhouse.Based on the static chamber-gas chromatography technique,fluxes of the main greenhouse gases(CO2,CH4 and N2O)were studied in four typical larch forests(moss-Dahurian larch forest,Ledum palustre L.-Dahurian larch forest,grass-Dahurian larch forest and rhododendron-Dahurian larch forest)and their relations with the physical and chemical properties of soil.The purpose of this study was to explore the characteristics of emission fluxes of CO2,CH4 and N2O in four forest types in this region and their relationship with the physical and chemical properties of soil,thus providing a theoretical basis for the overall accounting of greenhouse gas emissions in this region.The main results are as follows;1.The forest structure in this area is simple,the tree species is single,but the shrub layer,the herb layer and the ground floor are significantly different.In the four forest types,perennial water of moss-Dahurian larch forest,sporadic distribution of Dahurian larch forest and has the smallest density of forest;Ledum palustre L.-Dahurian larch forest has the largest densities of.forest and the smallest average breast diameter.Grass-Dahurian larch forest is 'located on the hillside,the soil layer is thin,and Dahurian larch forest is more folded,resulting in a smaller forest density,but the average breast diameter is the largest.Rhododendron-Dahurian larch forest is located at the highest elevation,and the shrub is dominated by rhododendron,which is the only forest type associated with the dwarf pine.2.The four larch forests were all sources of CO2,with average fluxes of 45.88(moss-Dahurian larch forest),38.68(Ledum palustre L.-Dahurian larch forest),54.54(grass-Dahurian larch forest)and 62.98(rhododendron-Dahurian larch forest)mg m-2·h-1,respectively.Rhododendron-Dahurian larch forest has the highest flux.Ledum palustre L.-Dahurian larch forest has the smallest flux.Temperature is the main limiting factor of soil CO2 emission flux in this region,and the influence of soil moisture content and pH value on the CO2 emission flux of soil is different from the four forest type.Because of the high altitude,low average temperature and short growth cycle,the overall level of CO2 emission in this region was keep low value.3.Under each forest type,there was a significant positive correlation between soil CO2 flux and soil temperature.The average CH4 fluxes of the four types were 0.089(moss-Dahurian larch forest),-0.037(Ledum palustre L.-Dahurian larch forest),0.004(grass-Dahurian larch forest)and-0.03(rhododendron-Dahurian larch forest)mg·m-2·h-1,respectively.Moss-Dahurian larch forest and grass-Dahurian larch forest were sources of CH4,while the other two types were sinks of CH4.Moss-Dahurian larch forest contributed more than 95%of the CH4 emissions of this region.The CH4 emissions from grass-Dahurian larch forest and rhododendron-Dahurian larch forest were significantly correlated with soil temperature.The CH4 emissions from moss-Dahurian larch forest and Ledum palustre L.-Dahurian larch forest had a significant negative correlation with soil organic carbon.4.Among the four forest types,only rhododendron-Dahurian larch forest had a significant correlation between soil moisture at 5 cm soil depth and soil CH4 flux.The average N2O fluxes of the four types were 0.0073(moss-Dahurian larch forest),0.012(Ledum palustre L.-Dahurian larch forest),0.0093(grass-Dahurian larch forest)and-0.0003(rhododendron-Dahurian larch forest)mg·m-2·h-1,respectively,indicating that these forests are sources of N2O(except rhododendron).The N2O fluxes of the four forest types in this region were mainly concentrated in the late summer and in the autumn.The environmental factors influencing N2O flux differed between forest types.Grass-Dahurian larch forest presented a significant positive correlation between soil temperature at 10 cm soil depth and N2O flux,and a significant negative correlation between N2O flux and total nitrogen,alkali-hydrolyzable nitrogen and organic carbon.Rhododendron-Dahurian larch forest had a significant positive correlation between N2O flux and both soil temperature and soil moisture.The N2O flux in the Moss-Dahurian larch fotest and Ledum palustre L.-Dahurian larch forest presented a significant correlation with soil total nitrogen and organic carbon,respectively,but showed no significant correlation with soil temperature,moisture or pH value. |
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