Carbon Fixation Technology Of Soil Aggregates Under Different Land Use Patterns In Danjiangkou Reservoir Area

The change of land use pattern is an important part of global ecological change.Different land use patterns will change the basic physicochemical properties of soil due to the change of the direct vegetation type.These changes will affect the carbon cycle in soil by changing soil structure and organic matter turnover.As the basic structural unit of soil,the influence mechanism of carbon turnover and fixation in soil aggregates is not clear after the change of land use pattern.In this study,three common land use patterns(dry land,paddy land and forest land)in Danjiangkou reservoir area were selected as the research object,and the effects of changes in land use patterns on the stability of soil aggregates and the distribution characteristics of carbon,nitrogen and their stable isotopes in soil aggregates were investigated.At the same time,indoor culture experiments were used to study the respiration characteristics of soil aggregates in different land use modes and the changes of carbon stable isotopes in their products.The main conclusions are as follows:(1)Stability of soil aggregates in different land use typesUnder the condition of dry sieve,the mechanical stability of soil aggregates under different land use types was dry land > paddy field > forest land.Under the condition of wet sieve,the water stability of aggregates showed the opposite trend to the mechanical stability,that is,forest land > paddy field > dry land.The results of percentage of aggregate destruction(PAD)show that the damage rate of aggregate was dry land > paddy field > forest land,which shows that although the mechanical stability of dry land was high,it was also easy to break large aggregate into small aggregate when encountering rain erosion,which leads to more soluble carbon loss along with rain and aggravates the damage of soil erosion.Forest land is better able to resist rain erosion and reduce carbon loss.(2)Soil aggregates carbon and nitrogen distribution characteristics under different land use patternsUnder the three land use patterns,the content of organic carbon was forest land > paddy field > dry land,and the content of total nitrogen was paddy field > forest land > dry land.From different aggregates,the content of organic carbon and total nitrogen in soil aggregates decreased with the increase of aggregate size.For the ?13C value,the ?13C of different land-use patterns was basically dry land > forest land > paddy field,and there was no significant difference between different soil aggregates.For the soil ?15N value,the ?15N of different land use patterns was forest land > paddy field > dry land,and the ?15N value of different aggregates generally decreases with the increase of aggregate size.The change of land use mode had a great influence on urease and sucrase activity,but a little influence on catalase activity.Urease activity was in the order of woodland > dryland > paddy field;invertase activity was in the order of paddy field > woodland > dryland;catalase activity was in the order of paddy field > dryland > woodland.Soil organic carbon had a significant positive correlation with urease and invertase,soil p H had a significant negative correlation with invertase and catalase,while soil total nitrogen had no significant correlation with three enzyme activities.(3)Response of soil aggregates respiration process to land use pattern and temperatureThrough soil incubation experiment,it was found that the soil respiration rate of different land use types was forest land > paddy field > dry land.The soil respiration rate of all treatments increased significantly with the increase of incubation temperature.There were also differences in the soil respiration rate of different aggregate sizes,and the difference was more obvious in the forest soil.The main characteristics were that the respiration rate of < 1mm aggregates was significantly higher than that of > 1mm aggregates.Using ?13CO2 value to analyze the contribution of CO2 source of soil respiration,it was found that in the initial stage of incubation experiment,the soil respiration rate was mainly dominated by inorganic carbon respiration,and with the extension of incubation time,the soil respiration was dominated by microbial respiration in the later stage of incubation.In summary,the carbon fixation process of soil aggregates under different land use methods in this study area is significantly different.Soil aggregates are more stable in woodland than agricultural land(paddy fields and dry land),and forest land is more resistant to rain erosion and reduces the loss of carbon in the soil.The carbon and nitrogen contents of soil aggregates under different land use patterns showed that forest land and paddy field were significantly higher than dry land,indicating that the carbon fixation capacity of forest land was higher than that of agricultural land.Among agricultural land,paddy fields are significantly higher than dry land.The soil respiration rate is forest land> paddy field> upland,indicating that different land use patterns will affect the respiration rate of soil aggregates by changing the carbon content in the soil,and thus affect the process of the transfer of fixed carbon in the soil to the atmosphere.