Impacts Of Climate Change And Shrubification On Carbon Cycle In Desert Steppe

The changes of climate and land-use will affect the material and energy cycle processes of terrestrial ecosystems.Global greening caused by human activities has been focused by scientists worldwidely.Large-scale afforestation conduced by ecological management projects in China is one of its driving factors.Under the given background,the feedback mechanism of carbon-water cycle in terrestrial ecosystems still need more study.Vegetation structure and function has changed a lot in ecological restoration projects while experiencing the global climate change,which inevitably caused profound impacts on the carbon cycle of the zonal desert steppe ecosystem that affected by artificial shrubification.Studying the impacts of climate change and artificial Caragana intermedia shrubification on carbon storage and exchange in desert steppe can not only reveal the carbon-water cycle response mechanism of terrestrial ecosystems under this background,but also can provide regional scientific basis for ecological management.Thus,this research used simulation and observation methods such as ecosystem process model and eddy covariance technique to explore the changes of carbon storage and exchange of desert steppe ecosystem in Yanchi County under the background of climate change and artificial shrubification in a long-term sequence.The main results of this study are as follows:(1)Based on the meteorological data from 1958 to 2017,climate scenarios simulation and Biome-BGC ecosystem process model,this study simulated the carbon storage of desert steppe in four different climate change scenarios.In these climate scenarios,the annual average total carbon storage of the desert steppe ecosystem in Yanchi County is 2.3208-2.3652 kg/m2.Soil carbon storage accounts for the highest proportion of total carbon storage,followed by litter carbon storage and vegetation carbon storage.The interannual fluctuation of vegetation carbon storage is more significant,which is also consistent with the fluctuation of precipitation in the same period,and total carbon storage shows a rising trend in fluctuation.Temperature increment will cause a slight decrease in various types of carbon storage,while the increase in precipitation will result in a significant increment in various types of carbon storage.Interaction of precipitation and temperature will increase carbon storage eventually;In addition,litter carbon storage is the most sensitive kind of carbon to climate change,followed by vegetation carbon storage and soil carbon storage.(2)This study used Logistic growth model to modelized the growth process of Caragana intermedia in desert steppe,then combined with Biome-BGC model to simulated the impacts of growth process on the carbon storage in this ecosystem.The results showed that after artificial shrubification,vegetation carbon storage increased from 0.0524 kg/m2 to 0.3143 kg/m2,litter carbon storage increased from 0.0727 kg/m2 to 0.1278 kg/m2,soil carbon storage increased to 1.9634 kg/m2,while total carbon storage increased to 2.4055 kg/m2 in desert steppe ecosystem in 60 years.The proportion of litter and vegetation carbon storage to total carbon storage increased from 6.04%to 18.38%,in contrast,the proportion of soil carbon storage decreased from 93.96%to 81.62%.It can be seen that planting shrub not only can increase the carbon storage in desert steppe ecosystem,but also can change the proportion of each carbon storage components.(3)This paper studied the impacts of artificial shrubification on carbon exchange characteristics in ecosystem-scale by using the open-circuit eddy covariance data which collected by Yanchi station in 2017.The results indicated that the daily change of carbon flux in this ecosystem shows a "single peak" form,which means that desert steppe ecosystem was a carbon sink from 8:00 am to 6:00 pm,and will become carbon source at night;The characteristics of seasonal changes showd that this ecosystem was a significant carbon sink from May to September,and gradually changed into a carbon source with the end of the growing season;the Net Ecosystem Exchange(NEE)between ecosystem and the atmosphere is-156.97 gC/m2,which means that the desert steppe ecosystem in Yanchi County was a carbon sink.(4)Based on the comparison of soil respiration dataset between grassland and Caragana intermedia shrubbery in 2019,this paper studied the effects of artificial shrubification on the carbon exchange between soil and atmosphere in desert steppe ecosystem.The soil respiration of grassland and Caragana intermedia showed a "single peak" shape during the day,which means that they were consistent with the changement of daily temperature,meanwhile,the soil respiration of Caragana intermedia shrubbery was greater than that of grassland at the same time and shows a significant difference.The peak value of grassland soil respiration in the growing season is 1.8515μmol/m2·s,while peak value of soil respiration under Caragana intermedia shrubbery is 2.2872 μmol/m2·s.It can be seen that artificial shrubification will accelerate the soil respiration rate in desert steppe and enhance the carbon exchange between soil and atmosphere.