Study On Temporal And Spatial Variation Characteristics Of Vegetation Index And Soil Carbon Dioxide Flux In The Eastern Wushaoling Of Qilian Mountains

Qilian Mountain is an important ecological security barrier in the inland area of northwest China,and its ecological environment has been widely concerned.To this end,on the basis of carrying out on-site monitoring of soil CO₂ flux and vegetation sample survey in the alpine region of Wushaoling Plateau in Qilian Mountains,this paper extracted the regional vegetation coverage through pixel dichotomy model based on MODIS-NDVI remote sensing data set and corresponding climate data list from 2005 to2018.The response of NDVI to climate factors,the distribution characteristics of soil CO₂flux and its driving factors were also discussed.The main conclusions are as follows:(1)During the growing season from 2005 to 2018,MODIS-NDVI remote sensing data showed obvious inter-annual and inter-monthly variation characteristics.In 14 years,NDVI of vegetation rose from 0.4707 in 2005 to 0.5193 in 2018,showing an overall increasing trend;from May to September,NDVI of vegetation increased first and then decreased gradually,reaching the peak value of 0.562 in July and falling to 0.483 in September.(2)The results of spatial distribution of vegetation coverage displayed that the vegetation coverage in the eastern part of Wushaoling was relatively high during the growing season,and the area covered by middle and high grade vegetation accounted for65.96%of the study area,which was slightly higher than the overall average level of Qilian Mountains.Among them,the medium and high grade vegetation coverage is mainly distributed in Wushaoling Nature Reserve and its southwestern Tanshanling area,while the low vegetation coverage is mainly distributed in the southeastward Huazang Temple and Songshan Town.(3)Based on the meteorological data from 2005 to 2018 and Pearson correlation analysis,it was found that there was a significant positive correlation between the annual average NDVI of vegetation and the average annual rainfall(RN,P=0.621,PN,P<0.05),which was weakly correlated with the annual average temperature,dew point temperature,atmospheric pressure and relative humidity,indicating that rainfall was the main factor affecting vegetation NDVI in the region,and the response of NDVI of vegetation to climate factors had a certain lag.(4)Through the statistical analysis of the monitoring data of soil CO₂ concentration at 41 points in the Wushaoling area,it was found that there were significant differences in the soil CO₂ concentration and CO₂ flux at different soil depths.Among them,there was an obvious positive correlation between soil CO₂concentration and soil depth(R=0.88,P<0.001).The CO₂ concentration increased from 215?312 ppm at 0 cm above the ground surface,and 256.00?846.00 ppm at-5 cm to 308.00?1496.00 ppm at-15 cm.At the same sampling point,the soil CO₂ flux was the largest in the range of 0?-10 cm and-5?-10 cm,reaching 1.02?mol·m^-2·s^-1 and 1.32?mol·m^-2·s^-1 respectively;different sampling points There was a significant negative correlation between soil CO₂ flux at different sampling points and altitude(R=-0.89,P<0.001).As a whole,the mean value of the regional soil carbon fluxes decreased by about 0.04?mol·m^-2·s^-1 for every 100 m above sea level.