Vertical Distribution Of Forest Soil Carbon And Nitrogen And Its Response To Hydrothermal Changes In The Permafrost Region Of The Greater Xing'an Mountains

The change of the Carbon and nitrogen content,which the carbon and nitrogen cycle of variation in forest.Exploring the changes in soil carbon and nitrogen content of forest ecosystems in permafrost regions is of great significance for the exploration of their carbon and nitrogen storage and the response mechanism to climate change.This study selects the widely distributed and representative Larix gmelinii forests,Betula platyphylla forests,and Betula-Larix mixed forests in the Greater Xing'an Mountains as background.Using indoor simulation experiments of artificially controlled water and heat conditions,collecting 0-30 cm shallow forest soil,simulating the most active carbon and nitrogen components:organic carbon(SOC),soil soluble organic carbon(DOC),soil total nitrogen(TN),soil ammonium nitrogen(NH₄⁺-N)and soil nitrate nitrogen(NO₃^--N)in shallow forest soils after extreme precipitation(humidification)during the growing season(warming),and the short-term dynamic response to changes in water and heat conditions,and systematically studies and analyzes the spatial heterogeneity and short-term volatility of forest soil carbon and nitrogen content.The main conclusions of this research are as follows:(1)Vertical distribution characteristics of soil carbon and nitrogen under different forest types.Although there are differences in soil carbon content among the three forest types,they are not significant.The average soil carbon content of the three forest types is the highest in the Betula platyphylla forests,and the results of the analysis of variance show that there is no significant difference in the SOC and DOC content between the forest types(p>0.05).The soil SOC in the vertical direction of the three forest types of soil presents that the surface layer is larger than the bottom layer,and the vertical distribution of soil DOC presents a phenomenon of 0-10cm>20-30cm>10-20cm;The results of analysis of variance showed that there was no significant difference in SOC and DOC content among the three forest types in each soil layer(p>0.05).The soil nitrogen content is the highest in the Larix gmelinii forest,and the vertical distribution shows that the surface layer is larger than the bottom layer.There were significant differences in TN content among the three forest types(p<0.05),and there was no significant difference in NH₄⁺-N and NO₃^--N soil layers(p>0.05).(2)Dynamic changes of soil carbon and nitrogen in different forest types under the interaction of water and heat.The overall soil carbon content decreases with the increase of temperature,increases with the increase of moisture,and decreases with the passage of cultivation time.The average value of SOC content in different forest types was the same as before cultivation;temperature had a significant effect on soil SOC content of Larix gmelinii forest and Betula-Larix mixed forest(p<0.05),and the SOC content increased with the increase of water;The DOC content in the three forest types was significantly affected by temperature and moisture(p<0.05).As the temperature increased,the DOC content showed a downward trend and increased with the increase of moisture.The soil nitrogen content generally fluctuates and decreases with the passage of time,and decreases with the increase of soil depth in the vertical direction.The TN content in Larix gmelinii forest is significantly affected by temperature and moisture(p<0.05),and decreases with the increase of temperature and moisture.The NH₄⁺-N and NO₃^--N content of the three forest types generally show an increase first and then later over time The downward trend increases with the increase of temperature and moisture.(3)Influencing factors of forest soil carbon and nitrogen dynamic changesThe change of soil carbon and nitrogen is the result of the interaction of soil physical and chemical factors.SOC?Water content and TN are the key factors for the change of soil carbon and nitrogen.Temperature and moisture have significant effects on the soil carbon and nitrogen of the three forest types by changing the living environment of soil microorganisms.Temperature mainly has a significant influence on the content of soil SOC,DOC,TN and NH₄⁺-N,and moisture mainly has a significant influence on the content of soil DOC,TN and NO₃^--N.The interaction of the temperature and moisture has a significant impact on the DOC content of the Betula-Larix mixed forest.