| Soil dissolved organic carbon(DOC)are defined as the carbon extracted by water or salt solution and filtering through filtermembrane with 0.45?m,which is one of the most active components in soil.Because of its characteristics of oxidation,decomposition and mineralization,it has a certain influence on transportation and transformation between organic matter and inorganic matter,mineral weathering,microbe activity,and soil nutrient cycling.It can be easily adsorped by mineral soil,but also transfers with soil moisture into the water environment.Absorption is an important process that affects the transportation and transformation of DOC in soil.Studies on DOC adsorption are crucial to elucidate the cycling and transformation of soil organic carbon and soil nutrient circulation.In recent years,with the indepth study of the carbon cycle of terrestrial ecosystems and global climate change,the study of soil soluble organic carbon has become one of the hot spots in the soil,environment and ecology.At present,studies on soil soluble organic carbon adsorption mostly focused on forests,grasslands and wetlands,and most of the research methods are using the iso-temperature adsorption test under oscillation,but there is no report on the dynamic research of saline-alkali paddy field on soluble organic carbon adsorption under natural conditions.This research area is located in Songyuan of western Jilin Province,which belongs to the climate-sensitive and ecologically fragile areas.After decades of farmland development,the region has formed a special salt-alkali farmland ecosystem,which has become an important grain production base in China.Based on the National Natural Science Foundation of China,"Study on Soil Organic Carbon-Inorganic Carbon Transfer Fluxes and Transformation Mechanism in Saline-Alkali Soils of Western Jilin Province",we chose five saline-alkali paddy farmlands(P1,P2,P3,P4 and P5)for the research.Topsoil(0-20cm)and subsoil(20-40cm)samples were taken for70-day indoor simulation experiments under stationary conditions,The experiment studied the DOC adsorption characteristics under different solution concentrations and analyzed the effects of physical and chemical properties on DOC maximumcumulative adsorptions.The results showed that the soil adsorption rate was large in earlier period while decreased with time,which could be described by the Elovich equation suitable to DOC adsorption under different solution concentrations.The Freundlich equation were best fitted with DOC isometric adsorption features,from which the coefficients indicated that adsorption capacity of soils significantly differed from each other,the adsorption capacity of paddy fields was the highest at P1 and P3 site,medium at P4 and P5 site and the lowest at P2 site.The adsorption capacity of surface soil was greater than the bottom layer in the same site.Correlation analysis of soil physico-chemical properties and DOC maximum cumulative adsorption showed that the physical properties of soil,such as clay content,was the major factor affecting soil adsorption capacity.The higher clay content of the soil,the greater DOC maximum cumulative adsorption.The chemical properties of soil,such as pH and exchangeable sodium percentage,were the important factors affecting soil adsorption capacity.There was a significant negative correlation between DOC maximum cumulative adsorption,and with the increase of the initial DOC concentration,a significant negative correlation was shown.The organic matter content promoted the soil adsorption of DOC,but with the increase of DOC added liquid concentration,the promotion effect was relatively reduced.This study were crucial to elucidate the cycling and transformation of DOC on saline-alkali paddy fields and it provided a scientific basis for understanding DOC's adsorption behavior in different soil environment. |
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