| In order to study the effect of soil freezing and thawing on carbon and nitrogen turnover in spring and autumn,five kinds of forest soils in Changbai Mountain area were taken as the research object.In situ cultivation continuous sampling method was used to determine and analyze soil microbial biomass carbon(MC)and nitrogen.Dynamic changes of(MN),ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3--N),total soluble carbon(TSC)and nitrogen(TSN)during freezing and thawing in spring and autumn and nitrogen ore The spatial and temporal dynamic patterns of chemical and nitrification.The results showed that:1.During the freezing and thawing process of soil in spring and autumn,the temporal dynamics of soil microbial biomass carbon and nitrogen in the five forest types varied dynamically,and the soil microbial biomass carbon and nitrogen showed obvious vertical spatial heterogeneity.Except for some periods,soil microbial biomass N in 0-10 cm layer was significantly higher than that in 10-20 cm layer,and soil microbial biomass C in 0-10 cm layer was also significantly higher than that in 10-20 cm soil layer.2.During the spring thawing process,the temporal dynamics of soil TSN content in the 0-10 cm layer of the 5 forest types are basically the same.The maximum TSN release in the spring thaw period occurs in the middle and later stages of thawing,while the maximum TSN release in the autumn freezing season occurs.In the late thawing period,the soil in the lower layer of the thawing season maintains good consistency with the upper layer.In the autumn freezing season,in addition to the individual period of Korean pine broad-leaved forest,good consistency was maintained in the upper layer of soil.In the spring thawing process,the TSC content in all five forest types increased first and then decreased.During the freezing process in autumn,the consistency of the TSC content in the upper and lower layers of the soil was kept consistent in some periods.3.According to the time characteristics of NH4+-N and NO3--N released during the spring thaw,the upper layers of the five forest types basically exhibit the same pattern,that is,NH4+-N reaches a relatively large peak in the middle and later stages of thawing and NO3--N At the end of the thawing period,the maximum accumulation amount was reached,and the dynamic change of soil in the lower layer of NO3--N was consistent with that in the upper layer.The time characteristics of NH4+-N and NO3--N released during the freezing period in the five forest types of soil also showed the same pattern.The NH4+-N content of each forest type peaked in the middle and later stages of freezing,and the NO3--N was frozen in the freezing stage.The final release reaches the maximum release.4.During the spring thawing process,net nitrogen mineralization was intense during the mid-thawing period in broad-leaved forest,Changbai pine forest,Korean pine broad-leaved forest,and secondary birch forest.Quercus mongolica forest was intense in the middle and later stages of freezing.The net N mineralization rate of Changbai Pine and Korean pine broad-leaved forests was lower than that of the other three forest types.There was no significant vertical difference in net N mineralization between upper and lower layers of the five forest types during the entire thawing period.During the freezing season in autumn,the positive net N mineralization increased during the five forest types compared to the spring thawing season.The broad-leaved forests experienced positive and negative fluctuations in mineralization throughout the freezing period,and the net N mineralization rate was low in certain periods.The secondary mineralization of the Betula platyphylla,Pinus koraiensis broad-leaved forest,and Quercus mongolica forests resulted in severe mineral nitrogen mineralization at the end of the frost period,which increased the net nitrogen mineralization. |
PDF Full Text Request