Effects Of Different Litters On Soil Organic Carbon Transformation In Ejin Horo Banner

China is a country seriously affected by salinization,which will degrade the land and adversely affect the soil properties and plant growth,and the carbon utilization and carbon cycle in saline soils is a hot topic of current research.Dissolved organic carbon（DOC）,as an important component of soil organic carbon,is characterized by fast movement and easy reaction,and can directly participate in the carbon cycle.The decomposition of saline litter will release DOC,which is an important source of soil organic carbon in saline soils.Salinity stress leads to less vegetation cover on the soil surface,and the process by which litteric material is imported into the soil in the form of organic carbon and then decomposed by microorganisms into inorganic carbon and release CO₂is called soil carbon mineralization,which is one of the important means to study the process of carbon flux transfer.DOC that enters the soil via leaching or other routes is sorbed and fixed into the soil,which in turn is converted into organic carbon.The sorption and retention of DOC by soil will directly affect DOC mobility and biological effectiveness,which will have significance on soil organic carbon pool.In this study,we collected litteric and soil samples of five saline plants,namely,Suaeda glauca Bunge,Kalidium foliatum,Tamarix chinensis,Achnatherum splendens,and Phragmites australis.from a representative saline site in Ejin Horo Banner,Ordos City,Inner Mongolia,and all of them were tested indoors for DOC release from decomposition of litteric material,soil organic carbon mineralization and soil DOC adsorption.The dynamic changes of DOC release during decomposition were observed through litteric decomposition tests under controlled temperature and p H conditions,and the effects of organic carbon mineralization and soil adsorption tests on mineralization as well as adsorption processes were clarified under controlled salinity and p H conditions.To investigate the decomposition dynamics of litter in saline soils,reveal the organic carbon mineralization process of saline soils,and clarify the sorption behavior of saline soils on DOC.To provide a theoretical basis for the carbon cycle of saline soils,the calculation of salt storage and nutrient flow.The main research findings are as follows:（1）The highest DOC release from the five saline litter species was from Kalidium foliatum(618.50 mg·kg^-1),and the lowest was from Achnatherum splendens(240.59mg·kg^-1).At a certain temperature,the DOC release from Suaeda glauca Bunge,Kalidium foliatum and Tamarix chinensis basically showed a tendency to become larger with increasing p H,and the opposite was true for Achnatherum splendens and Phragmites australis;meanwhile,the decomposition rate of Kalidium foliatum or Suaeda glauca Bunge litter was significantly higher than that of Achnatherum splendens litter（P<0.05）.At a certain p H,the content of DOC released from the decomposition of the five species increased with increasing temperature,and the weight loss rate and decomposition rate of litter also increased and accelerated with increasing temperature,while the half-life and full-life became shorter.Initial whole carbon content,C/N,and lignin/N showed a significant（P<0.05）positive correlation with weight loss rate.The initial total nitrogen,lignin and cellulose contents showed significant（P<0.05）negative correlation with weight loss rate,while the initial total phosphorus and potassium contents were not necessarily related to weight loss rate.（2）Soil mineralization rate and mineralization accumulation were significantly（P<0.05）increased by the addition of litter.The maximum mineralization rate(212.76mg·g^-1·d^-1)was highest in the soil with the addition of Suaeda glauca Bunge litter under the same salinity conditions.The highest accumulation of soil organic carbon mineralization was observed with the addition of Suaeda glauca Bunge(2.331 g·kg^-1)and Kalidium foliatum(2.424 g·kg^-1)litter under different salinity conditions.Elevated salinity promoted the accumulation of organic carbon mineralization in soils with 20-40cm of Achnatherum splendens litter and inhibited it in soils with 0-20 cm.Under different p H treatments,the accumulation of organic carbon mineralization in soil supplemented with Suaeda glauca Bunge litter 20-40 cm was highest at p H 9 and p H10.5(2.344 and2.351 g·kg^-1,respectively).The lowest organic carbon accumulation mineralization(1.440 g·kg^-1)was observed at p H10.5 in soils with added Phragmites australis litter（P<0.05）.Tamarix chinensis had the lowest Cp/SOC（0.154）and the strongest carbon sequestration capacity,while Phragmites australis had the highest Cp/SOC（0.333）and the weakest carbon sequestration capacity.Redundancy analysis showed that litteric cellulose and total nitrogen were significantly positively correlated with organic carbon mineralization accumulation under different salinity conditions（P<0.05）,and soil ESP,conductivity,and p H were significantly negatively correlated with organic carbon mineralization accumulation（P<0.05）.Under different p H conditions,soil total organic carbon,total nitrogen,litter lignin/nitrogen,and carbon/nitrogen were significantly positively correlated with organic carbon mineralization accumulation（P<0.05）,and ESP,powder particles and soil mineralization accumulation were significantly negatively correlated（P<0.05）.（3）The soil sorption of all five litter types increased with time and the concentration of DOC addition solution.Under different salinity conditions,the soil sorption of all five litter types was highest at S3（P<0.05）,the soil sorption of Kalidium foliatum,Suaeda glauca Bunge,and Phragmites australis types was lowest at S9 treatment（P<0.05）,and the soil sorption of Achnatherum splendens and Tamarix chinensis litter types was lowest at S1 treatment（P<0.05）.The soil sorption of all five litter types under different p H conditions was lowest at p H10.5（P<0.05）.The first-level kinetic equation was able to simulate the sorption kinetic process well（R²above 0.955）.Under different salinity conditions,the rate of DOC adsorption（k 0.282,0.291,and 0.267,respectively）was the fastest in the soil of Tamarix chinensis litter type under S1 treatment when the concentration of the added solution was 50,100,and 300 mg·L^-1.The rate of DOC adsorption（k was 0.327,0.239）was the fastest in the soil of Kalidium foliatum litter type under S1 treatment when the concentration of the addition solution was 200 and 400mg·L^-1,respectively.The rate of DOC sorption was fastest in the litteric types of Achnatherum splendens（k=0.346）and Kalidium foliatum（k=0.383）soils under different p H treatments when the concentration of the addition solution was 100 and 200 mg·L^-1.The Langmuir equation was able to model the isothermal sorption process well（R²above0.955）.Correlation analysis showed that the highest cumulative soil sorption was related to soil total nitrogen,conductivity,Na⁺,and Mg²⁺under different salinity conditions.Under different p H conditions,soil p H,conductivity,Na⁺,Mg²⁺,and Ca²⁺were the main factors affecting the maximum cumulative soil sorption.（4）All five species of litter contained polysaccharides and proteins,and the positions of absorption peaks did not shift significantly before and after decomposition,and the corresponding substance species remained unchanged.The polysaccharides and proteins in Suaeda glauca Bunge,Kalidium foliatum and Phragmites australis litter were higher after decomposition than before decomposition under different p H treatments.The positions of absorption peaks before and after soil mineralization did not shift significantly,and the substances corresponding to absorption peaks were aromatic compounds,polysaccharides,and lignin compounds and all of them changed under different treatments compared with the initial ones.The types of functional groups in the soil before and after adsorption did not change,and both had aromatic compounds,polysaccharides,and aliphatic compounds.