Process Of Soil Organic Carbon Responses To Warming And Precipitation Enhancement Under Different Utilizations In An Alpine Steppe

Grassland use and management practices have a very important impact on many soil ecological processes,which often determine the change degree and direction of soil organic carbon process(SOC,soil C storage and C emission).Thus understanding the effect of grassland use on soil C process is very important to scientifically manage and optimize grassland,and promote the sustainable development of regional agriculture and animal husbandry.The paper showed that soil samples were collected from different plots of conversion of steppeto farmland(GF),grazed steppe(GG)and ungrazed steppe(UGII)in a long-term field experiment in the alpine steppe region of Northwest China.This project tries to analyze the different of SOC process under different grasslanduse types,and to study the effect of different soil C fractions and soil aggregates.In addition,this paper also tries to discuss the change trend of SOCanduse adenitrification-decompositiond(DNDC)model to predicting SOC dynamics under grassland use in the Bayinbuluk alpine steppe.Results showed that:(1)The mean total carbon content was50.03 g/kg,60.41 g/kgand 59.77 g/kg at the 0-20cm at GF,GG and UGIItreatment,respectively.The content of SOC was31.13 g/kg,43.94 g/kg and 42.81 g/kg at 0-20cm,respectively.Over the growing season(from April to September),the mean soil respiration(R_s)is 4.35?mol/(m~2·s),2.48?mol/(m~2·s)and 2.37?mol/(m~2·s)at the GF,GG and UGIItreatments,respectively.(2)Compared with GF treatment,Increased the percentage of soil water stable aggregates(diameter is>2mm)by 3.69 and 4.07 times,respectively.The soil aggregates and its include SOC showed that the soil aggregates particle diameter bigger and its include SOC higher.Soil organic carbon fractions(very labile C fraction,labile C fraction,less labile C fraction and stable C fraction)had a strong positive correlation with soil organic carbon content.Unstable organic carbon fractions content are the mian components at GF treatment,butstable organic carbon fractions content are the mian components at GG and UGIItreatments.(3)The accumulated of R_swas 4.90 mg/g,6.99 mg/g and 6.52 mg/g in the30?incubator(cultivationperiodwas156days)at GF,GG and UGII treatments,respectively.Very labile carbon fraction and stable carbon fraction showed positive correlations,while labile carbon fraction and less labile carbon fraction had negative correlations with accumulated of soil respiration.Laboratory incubations from precipitation enhancement(cultivationperiodwas 40 days)showed that change of soil water content had negative correlations with soil respiration rate.The accumulated of R_swas 1.825 mg/g,2.323 mg/g and 2.090 mg/g in the contents of soil water 60%treatment at GF,GG and UGII,respectively.In addition,the R_sdropped by 0.046 mg/(g·d)when the soil water content decreased by 10g.(4)The DNDC model(r,RMSE and M is 0.91-0.95,6.39%-7.99%and(-0.20)-0.11g/kg,respectively)simulation results showed that an A2 scenario,the SOC and R_swere 27.25 g/kg and 6.45?mol/(m~2·s),26.78g/kg and 6.71?mol/(m~2·s),and 26.32 g/kgand 8.67?mol/(m~2·s)in 2020s,2050s and 2080s at GF treatment,respectively.The content of SOC was 44.25 g/kg,44.85g/kgand 46.15 g/kg,and R_swas 3.48?mol/(m~2·s),3.90?mol/(m~2·s)and 3.56?mol/(m~2·s)in 2020s,2050s and 2080s at GG treatment,respectively.In a word,the perspective of ecological and environmental protection,reasonable grazing steppe is one of the effective ways to improve the resources of sustainable utilization.