| The emission of CO2,N2O,CH4 and other greenhouse gases in the soil affects the content of greenhouse gases in the atmosphere,and intensifies the process of global warming.Northern China is the most sensitive region to the impact of climate warming,and the warming trend is more obvious than other regions.In this paper,the emission characteristics of CO2,N2O and CH4 from five forest types of soils(Hardwood broad-leafed forest,Korean pine broad-leaved forest,Secondary birch forest,Changbai pine forest and Mongolian oak forest)in the process of freeze-thaw were studied by means of continuous sampling in situ culture and indoor freeze-thaw simulation test.The results show that:1?The fluxes of indoor simulation and in-situ culture during freezing-thawing showed that forest soil in 5 freezing-thawing period was the source of CO2.The influence of freezing and thawing process on the CO2 emission flux of five forest types is different.In the indoor simulation test,the upper and lower soil CO2 fluxes of different forest types have spatial vertical heterogeneity,which shows that the contribution rate of the upper and lower soil to CO2 emission is different.The changes of forest types,soil layers and freezing and thawing periods and the interaction of the three factors combination have significant influence on each period of simulated freezing and thawing flux of CO2 in forest soil.In the in situ culture test,the CO2 emissions of soil of 5 forest types were all at a low level in the early stage of freezing-thawing,and the CO2 emissions increased significantly with the deepening of the soil thawing level.2?The fluxes of indoor simulation and in-situ culture during freezing-thawing showed that the forest type soil in freezing-thawing period 5 was CH4 sink.The CH4 fluxes of different forest types were not significantly different in the indoor simulation test.The CH4 fluxes of different forest types were significantly affected by the changes of forest types,soil layers and freeze-thaw periods and the interaction of the three factors-In the process of in-situ freezing and thawing,the CH4 emission flux was in the state of net soil absorption for most of the period,and no similar trend was found among different forest types.3?The fluxes of indoor simulation and in-situ culture during freezing-thawing show that the forest soil in 5 freezing-thawing period is the source of N2O.The results showed that the N2O fluxes of five forest types were different under indoor simulation,but the N2O fluxes of in-situ freeze-thaw in spring were almost the same among forest types.The results showed that the N2O fluxes of the upper and lower soil layers were basically the same.The changes of forest type,soil layer and freeze-thaw period and the interaction of the three factors all significantly affected the N2O flux of each forest type during the simulated freeze-thaw period.In the in-situ culture experiment,the N2O emission flux of Secondary birch forest and Korean pine broad-leaved forest increased with the freezing-thawing process,the other three forest types have no obvious upward trend.4?The contribution rate of CO2 in the upper layer of soil was much higher than that in the lower layer,and the contribution rate of CH4 and N2O in the upper and lower layers was not consistent.The CO2 accumulation of five forest types was significantly higher than that of Quercus mongolica and Pinus sylvestris;the CH4 accumulation was significantly higher than that of other two forest types;the N2O emission of hardwood forest and secondary birch forest was significantly higher than that of other three forest types.During in-situ freezing and thawing in spring,the average flux of CO2 and N2O in secondary birch forest and Korean pine broad-leaved forest was significantly higher than the other three forest types,while the average flux of CH4 in Hardwood broad-leaved forest,Secondary birch forest and Korean pine broad-leaved forest was higher than the other two forest types.5?In the simulated freeze-thaw experiment,there was a significant positive correlation between CO2 flux and soil microbial biomass carbon,microbial biomass nitrogen,nitrate nitrogen,ammonia nitrogen and soluble organic nitrogen.6?In the in-situ freeze-thaw experiment in spring,except for the Hardwood broad-leaved forest,there was a significant negative correlation between CO2 flux and soil water content in five forest types,but there was a significant difference between CO2 emission and water sensitivity in different forest types;except for the Hardwood broad-leaved forest,there was a significant positive correlation between N2O flux and soil water content in five forest types,but the water sensitivity was different according to forest types.The emission fluxes of CO2 and N2O of the five forest types were quadratic function with the soil surface temperature. |
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