Responses Of Phenology And NPP For Desert Steppe Vegetation In Inner Mongolia To Climate Change From 2000 To 2017

Inner Mongolia desert steppe is distributed in the semiarid and arid areas,which is also located in both climate sensitive and ecological fragile districts.It is significance to analyze the impact of vegetation phenology on the primary productivity and carbon cycle of ecosystem under the background of climate change.Based on normalized difference vegetation index(NDVI)data from the MODIS dataset and meteorological grid dataset during 2000-2017,we studied the phenophase changes in the desert steppe of Inner Mongolia and the resulting changes in net primary productivity(NPP).Firstly,we analyzed the spatio-temporal variation of climate.We then studied the characteristics of spatio-temporal changes of different vegetation type phenophases and estimated the spatio-temporal changes in net primary productivity of the desert steppe vegetation by the Carnegie-Ames-Stanford Approach(CASA)model.Finally,we analyzed the relationship between desert steppe productivity,phenophases,and climate variables.The relationship between net primary productivity and phenophases is revealed to provide theoretical support for regional ecosystem management and ecological construction.The main conclusions are as follows:(1)From 2000 to 2017,the annual average temperature and seasonal average temperature in the desert steppe area of Inner Mongolia showed an increasing trend,and the spring temperature increased significantly at the rate of 0.58?/10a(P<0.05).The annual precipitation fluctuates greatly and shows an insignificant decreasing trend,while the seasonal precipitation shows an insignificant increasing trend except in summer.Spatially,annual average temperature and seasonal average temperature gradually warm from north to south,and annual precipitation gradually decreases from northeast to southwest.(2)The phenophases change trend of different steppe in Inner Mongolia were different during 2000-2017.SOS of each steppe type advanced significantly at a rate of 0.66-1.16d/a(P<0.05).Except for the desert steppe(-0.13d/a),other steppe types were characterized by delay at EOS,of which the meadow stepppe delayed significantly at a rate of 0.43d/a(P<0.05).The LOS for all steppe were lengthened,among which the desert steppe and meadow steppe lengthened significantly by 0.76-1.58d/a(P<0.05).The spring phenology in the Inner Mongolia desert steppe is mainly influenced by the temperature in the first three months before SOS(T_S3).For autumn phenology,the rise of average temperature in autumn(T_autumn)advanced EOS significantly,while precipitation in the first three months before EOS(P_E3)and in summer(P_summer)delayed EOS significantly.(3)The average annual NPP from 2000 to 2017 was 104.71g C/(m²·a)in study area,showing regional differences with an obviously decreasing trend from east to west.Net primary productivity in spring,summer,and the growing season increased insignificantly,while NPP in autumn showed an insignificant decreasing trend.The increase of precipitation in the growing season is beneficial to the accumulation of ecosystem NPP.The change of precipitation in the growing season is the main factor affecting vegetation NPP,and the increase of precipitation in spring and summer is conducive to NPP accumulation in the desert steppe of Inner Mongolia(4)There is a close relationship between vegetation phenology and NPP in desert steppe of Inner Mongolia:Advance of SOS was conducive to the accumulation of spring NPP,and the delay of EOS promoted the accumulation of autumn NPP.There was a significant correlation between the LOS and NPP during the growing season(P<0.05).