Simulation Of Carbon Dynamics In Forest-Steppe Ecotone Based On Multiple Models

The study of carbon dynamics in grassland ecosystem plays an important role in the field of global change.It is a significant scientific problem to evaluate the relationship of carbon source/sink and its response to climate change and human disturbance.The forest-steppe ecotone as one of the most sensitive areas in the ecotone has a potential indicator of climate change.In this study,we take the Saihanwula Nature Reserve as a study area,which is a typical forest-steppe ecotone.Based on the observed data and meteorological data,we used the CENTURY model and DNDC(Denitrification-Decomposition)model to analyze and validate local parameters,then simulate the carbon dynamics of grassland ecosystems under the background of climate change and natural protection conditions.The main conclusions are as follows:(1)Based on the large number local parameters which were tested and verified by the measured data and the literature data,the local CENTURY model and DNDC model could simulate carbon dynamics of the study area.Regarding simulation accuracy,the DNDC model with day step is higher than the CENTURY model with the month step and has more advantages on dynamic analysis.(2)In the past 55 years,the aboveground and belowground biomass in the study area were about 71.01gC/m2 and 601.96gC/m2 respectively,and the total biomass was 672.97gC/m2.The variation trend of aboveground biomass and total biomass was consistent with annual precipitation,but is not obvious with the annual average temperature..Precipitation is one of the most important meteorological factors that affect the biomass.(3)The total carbon storage in the study area had shown an increased trend since the 1960s with a sharply decline in 1968,1988 and 2006.The total carbon density is 73295.41kgC/hm2,the vegetation carbon density is 6729.69kgC/hm2,the soil carbon density(0-50cm)is 66565.73kgC/hm2,and the total carbon storage is 0.22TgC.(4)Grassland ecosystems of the Saihanwula Nature Reserve is a carbon sink during the last 55 years with 38 years are the carbon sink,the others are the carbon source.Specifically,carbon storage is 22108.24kgC/hm2 during 1961-2015 with an increased rate 401.96kgC/hm2.The study found that carbon sequestration and aboveground biomass,positive correlation,respectively(p<0.01).The correlation coefficient between carbon sink and aboveground biomass and precipitation were respectively 0.785 and 0.756;Carbon sink and carbon sequestration,potential evapotranspiration,and the average daily temperature were the significant negative correlation,respectively(p<0.01).The correlation coefficient between carbon sink and potential evapotranspiration and the average daily temperature were respectively-0.637 and-0.395.(5)Based on CENTURY model,in the next 30-50 years,The aboveground and belowground biomass and soil carbon storage would show a not apparent increasing trend.