Study Of Characteristics Of Soil Organic Carbon Mineralization In Saline-alkali Paddy Fields And Dynamic Simulation In Western Jilin Province

Soil respiration is the main form of soil and atmospheric carbon flux exchange in the global carbon cycle.Compared with inorganic carbon,the turnover rate of organic carbon is faster than that of inorganic carbon.The small changes of soil organic carbon(SOC)also lead to a significant change in atmospheric CO2 concentration,and its position is extremely important for the global carbon cycle.The carbon pool of farmland ecosystem is a vital part and the most active part of the global carbon pool.Under the changeable global climate,some extreme weather changes or natural disasters(such as rainstorm,drought,flood,etc.)will aggravate the formation and area of saline-alkali land.China is one of the most serious countries affected by the salinization of the soil,and this not only harms the growth and development of the crops,but also causes the physical deterioration of the soil,the salinity of the groundwater rised,the farmland reduced and the large barren area of the land.The mineralization process is one of the effective methods to study the SOC characteristics,and the SOC mineralization is an important process for the input of CO2 to the atmosphere,which is related to the change of soil organic matter and CO2 flux,and is also closely related to the soil quality and the atmospheric greenhouse effect.SOC mineralization is also one of the biochemical processes of microbial utilization and degradation of soil organic matter.Its mechanism is influenced by the chemical composition,soil temperature,moisture and texture of SOC.In-depth study on the respiration of salinized paddy soil in the process of carbon cycle has practical reference values for the study of the mechanism of global carbon cycle.In our study,we selected the soil of Qianguo irrigation district,which is located in the northwest of Jilin Province in northeast China and also in the hinterland of Songnen Plain,where a large number of saline-alkali fields have been transformed into rice fields and have typical saline-alkaline characteristics.Four paddy fields(P1,P2,P3 and P4)with different saline and alkali levels were selected.The emissionfluxes of soil CO2 gas were measured in 1th,4th,7th,10 th,14th,21 th,28th,35 th and 70 th days by field investigation and laboratory simulation experiments.Based on the basic physical and chemical properties of soil,the dynamic changes of CO2 flux during mineralization simulation culture in saline-alkali paddy field were analyzed,and the effect of soil salinization degree on the mineralization process of organic carbon was studied.The results showed that the organic carbon contents with different salinization treatments were significantly different,showing a significant negative correlation(r=-0.945),and a significant difference in SOC content between the surface layer and the deep soil(P < 0.05).There were some surface enrichment phenomena,and saline-alkaline degrees,depth of soil layers and soil types influenced the SOC content.The effects of exchangeable sodium percentage(ESP)on the content of SOC in deep layer were significantly higher than that in surface soils.The differences of SOC contents between different samples and depths mainly depends on the differences of ESP between them.The dynamic constant temperature(25 ±0.5 ?)of the 70-day SOC mineralization laboratory experiment showed that the mineralization rate of SOC decreased rapidly on the incubation period of the first 7 days.From the 7th day to the 35 th day,the decrease trends became slower and the mineralization rate remained basically unchanged.The mineralization rate of SOC gradually decreased to the lowest point just after 35 days.The accumulation of SOC(CO2-C)increased exponentially with time,and the trends of CO2-C accumulation in each sample were approximately the same.CO2-C increased with the prolongation of incubation time,and the earlier stage was stronger,the accumulation rate was faster and the same rate was about the same.On the 35 th day,CO2-C accounted for 81.97% to 83.83% of the whole incubation period,and at the end of the culture period,the accumulation rate was about to the end of the culture period.The accumulation of CO2 tends to be gentle and gradually approaches the end point of accumulation.The first order kinetic model can effectively characterize the accumulation of CO2 during SOCmineralization(R2> 0.98).Combined with soil physico-chemical properties and dynamic simulation results,variance analysis,correlation analysis and multiple comparisons were carried out with SPSS and Origin software.The results showed that the mineralization process of SOC was influenced by many factors.ESP was the main influencing factor of this process.Salinization of soil inhibits the speed of soil carbon cycle.With the deepening of salinization degree,the mineralizable potential value of soil organic carbon(C0)decreases.According to the results of Pearson correlation analysis,there was a significantly positive correlation between C0 and SOC,and a high negative correlation between C0 and ESP,while the change trends of C0 and SOC were basically the same.The results indicate that the degree of salinization of soil affects the mineralization potential of SOC by affecting SOC.The organic carbon turnover rate constant k was highly positively correlated with ESP,moderately positively correlated with EC and C0/SOC,and moderately negatively correlated with SOC and p H,indicating that the degree of salinization is the main factor affecting the turnover rate of organic carbon pool,followed by C0 / SOC.According to r C0/SOC(0.975)> r C0(0.895),it can be concluded that the salinization of soil has a greater effect on the carbon sink than the carbon source process.In general,with the increase of SOC content,the intensity of mineralization reaction and the complete degree of mineralization reaction of SOC increased,and the accumulation of mineralization reaction increases,on the other hand,it decreased with the increase of ESP extent.The results of this study could provide some data support and theoretical basis for the characteristics of carbon sink / source and carbon cycle mechanism in paddy fields under saline-alkali stress in western Jilin Province,and also provided a basic example for the study of global carbon cycle at a small scale.