Study On Soil Organic Carbon Mineralization And Temperature Sensitivity Of Forest And Wetland In Permafrost Regions Of The Huma River Basin

Warming will promote the mineralisation of soil organic carbon in permafrost zones,with a consequent increase in soil carbon dioxide emissions,resulting in a positive feedback between the global carbon cycle and climate warming.The extent to which the soil carbon pool in permafrost zones responds to increased temperatures in forests and wetlands also depends on the temperature sensitivity of soil organic carbon decomposition.Investigating trends in the temperature sensitivity of organic carbon mineralisation in the background of forest and wetland soils in the permafrost zone in response to warming is important for understanding carbon cycling processes in the permafrost zone.Based on this,this thesis selected forest and wetland soils in the Daxinganling permafrost region as the research object,and analysed the dynamic changes in the physicochemical properties and temperature sensitivity of organic carbon mineralisation in forest and wetland soils through indoor experimental incubation,and elucidated the response of soil Q₁₀ to temperature increase.The dominant factors affecting organic carbon mineralisation in forest and wetland soils were identified.The following main findings were obtained:（1）There are significant differences in the physical and chemical properties of forest soils and wetland soils.The average values of soil organic carbon,dissolved organic carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen and soil pH in wetland soil were 187.40 g·kg^-1,318.36 mg·kg^-1,5.71 mg·kg^-1,22.46 mg·kg^-1,4.27 mg·kg^-1 and 4.60respectively;The average values of soil organic carbon,dissolved organic carbon,total nitrogen,ammonium nitrogen,nitrate nitrogen and soil pH in forest soil were 84.40 g·kg^-1,216.70 mg·kg^-1,2.48 mg·kg^-1,17.01 mg·kg^-1,4.74 mg·kg^-1 and 5.16,respectively.The contents of soil water content,organic carbon,dissolved organic carbon,total nitrogen,and ammonium nitrogen in wetlands were significantly higher than those in forests.The pH value and nitrate nitrogen content of forest soil are higher than those of wetlands.Wetland and forest soils are mainly composed of silt,clay,and a small amount of sand,with the composition ratio of soil particles being:silt>clay>sand.（2）Both forest and wetland soil organic carbon emission rates have the same distribution pattern,showing that the rate of increase in soil carbon mineralisation is stronger at low temperatures（-1°C-3°C）than at high temperatures（13°C-17°C）with increasing incubation temperature,and that the rate of soil organic carbon mineralisation gradually stabilises with increasing incubation time in both forest and wetland soils.The maximum and minimum mineralization rates of organic carbon in forest and wetland soils were 3.55 mg·kg^-1·h^-1 and 9.86 mg·kg^-1·h^-1,respectively,and 0.36 mg·kg^-1·h^-1 and 0.28mg·kg^-1·h^-1,respectively.The highest cumulative release of organic carbon from forest and wetland soils occurred at 17℃,increased by 177.98%-201.51%and 191.48%-283.50%respectively compared with–1℃.（3）Soil background levels and soil organic carbon mineralisation rates are significantly correlated.The results of the linear regression analysis showed that the main controlling factors for the rate of organic carbon mineralisation and its mineralisation in forest and wetland soils were also inconsistent,where the dominant factor for the rate of organic carbon mineralisation and its mineralisation in forest soils was the organic carbon content,whereas the dominant factor for the rate of organic carbon mineralisation and its mineralisation in wetland soils was the soil water content.The results of multivariate analysis showed that culture temperature,land type,and their interactions significantly affected the cumulative mineralization of soil organic carbon（P<0.05）.（4）Soil Q₁₀ levels are higher in low temperature forests and wetlands than in high temperature areas.The sensitivity of forest soil organic carbon mineralization at low temperature range from 2.28-2.52,with an average value of 2.39.The sensitivity of soil organic carbon mineralization in wetland ranges from 2.31 to 3.21,with an average of2.71.The sensitivity of forest soil organic carbon mineralization in high temperature range from 2.10 to 2.24,with an average value of 2.17.The sensitivity of soil organic carbon mineralization in wetland ranges from 2.12-2.32,with an average value of 2.21.（5）Based on the results of this thesis,we found that forest and wetland soil background values have different effects on soil organic carbon mineralisation.Soil moisture content dominated the efficiency of organic carbon mineralisation in wetland soils,whereas organic carbon content dominated the efficiency of organic carbon mineralisation in forest soils.In addition,soil Q₁₀ was higher at low temperatures than at high temperatures.