| Among global climate change studies, carbon cycle of terrestrial ecosystem and the changesof other greenhouse gases are continuously import to scholars all around the world. However,most existing results focus on the trend of soil organic carbon (SOC) during the plant growingseason, without consideration of SOC change during freezing-thawing period. In addition, theexisting studies in freezing-thawing period are mostly limited in Sanjiang plain, Songnen plain,arable land under different mulch in northwestern of China, as well as the tundra of plateau. TheSOC research of saline-alkali soil paddy field in northern areais rarely reported. Researchmethods mainly adopt indoor simulation experiments withthe limits of freezing-thawingtemperature and cycling time. And impact mechanism of SOC is little during freezing-thawingperiod. It will get more comprehensive and accurate results if the SOC storage offreezing-thawing period is added into the annualstudy.Several technical methods are chosen to finish this study, such asremote sensing,environmental modeling, spatial analysis, laboratory testing and data analysis. Typical paddyfields, dry fields, meadows and saline-alkali soil are selected to study the dynamic change of soilorganic carbon, total nitrogen, soil enzyme activity during freezing-thawing period. The resultscan provide technical reference for the freezing-thawing study in northern area of our country.The temperature of-25℃,-5℃,5℃is chosen to carry out the experiments. Fourmechanisms are designed as following:-5~5℃FTC (12h-Freezing-12h-thawing-cycles),-25~5℃FTC,-5~5℃FT(120h-Freezing-120h-thawing) and-25~5℃FT. SOC and TN decreased as thesoil depth increased in all soil types and the correlation of the both indexes are high. But the twoindexes changes are different during the freezing and thawing period. Generally speaking, SOCchange trend is similar in surface soil (0-10cm,10-20cm and20-30cm) while the one in the flatis the same. The SOC is certain increasing duiring-25~5℃FTC except the SOC of saline-alkalisoil. The times of freezing-thawing is the main impact factor compares the temperature. The TNof paddy and dry fields is increased at the end of freezing-thawing-cycles and the situation isopposite in the grassland and saline-alkali soil. The temperature and times of freezing-thawingare also the main factors to impact TN changes. But the temperature unaffected TN at FT.The soil dehydrogenase increased after freezing-thawing except the one in grassland. Thepolyphenol oxidase decreased by the affect of freezing-thawing. The change of catalase is little in four typical soils. The urease has the increasing trend. The freezing-thawing effect obviouslyaffect the soil enzymes and certain difference exist in various soil.It is easy to get the high correlation between SOC, TN and soil enzymes by SPSS. Thecorelation indexes between the three ones of saline-alkali soil are similar. The correlation ofurease is the highest while the one of catalase is the lowest. The result is similar to the calculatinthrough SIMCA-P. The enzyme play an important role in decomposing SOC, catalyticingmicromass activity, stabilizing soil structure, affecting elements cycles. The soil enzymes is veryimportant to soil elements cycles by synthesizing,accumulating,restraining and decomposing.The soil environment is alternately change between anaerobic and aerobic circumstance as thechange of soil temperature and water. Soil enzyme changes and affect SOC and TN.Althugh SOC and TN increased under freezing-thawing effect, the change of SOCD (soilorganic carbon density) and TND (total nitrogen density) is little. The SOC storage increased infour soil and the storage sequence is paddy fields<saline-alkali<meadows <dry fields. The TNstorage is1.5×104~259×104t with different decrease under freezing-thawing.On the basis of the establishment of the underlying database of soil, vegetation and climatein western Jilin Province the annual greenhouse gas emissions (CO2, CH4, and N2O) aresimulated to assess the global warming potential of four land use types by using DNDC model.The GWP of IPCC is also selected to evaluate the GWP of four typical soils under differentfreezing-thawing to judge soil organic carbon sequestration. The dry fileds is carbon source. Thepaddy fields (-5~5℃FTC and-25~5℃FTC) is carbon source and the one (-5~5℃FT and-25~5℃FT) is carbon sink. The meadows(-25~5℃FTC) is carbon sink and the one in other conditionis carbon source. The saline-alkali soil (-5~5℃FTC and-25~5℃FT) is carbon sink. The GWP islow in northwest and high in the center of the studying area.The previous study of soil organic carbon is focus on the plant growing season. In this study,the experimental simulation techniques is used to study the mechanisms of soil organic carbon/total nitrogen/soil enzyme of different land use types under freezing-thawing effect in westernJilin Province. The results can be provides an example for studying soil organic carbon storage infreezing-thawing period.
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