Study On Spatial Heterogeneity Of Soil Organic Carbon And Total Nitrogen Of Alpine Grassland And The Influencing Factors In Qinghai-Tibet Plateau

Soil carbon and nitrogen play an important role in the terrestrial ecosystem carbon and nitrogen cycle.The Qinghai-Tibet Plateau is the main ecological area in China.The content and distribution of soil carbon and nitrogen is one of the important contents for evaluating soil fertility.In this research,we studied 93 samples of the alpine grassland in the Tibetan Plateau that north-south spaned 10 latitudes and east-west spaned 13 longitudes.Moreover,we analysed the spatial heterogeneity of soil organic carbon(SOC)and total nitrogen(TN)in 0-50 cm soil layers(0-10 cm,10-20 cm,20-30 cm and 30-50 cm).The results indicate that:(1)The contents of SOC and TN were mainly distributed in the soil surface(0-20 cm)Moreover,with the increase of soil depth,their contents also gradually decreased.In soil layers above 20 cm,the contents of SOC and TN belonged to medium spatial variation.However,in the soil layer below 20 cm,the SOC and TN content belonged to medium spatial variation and strong spatial variation,respectively.(2)The SOC of each layer had medium spatial correlation,affected by random and structural factors together.TN had strong spatial correlation in 20-30 cm soil layer,affected by structural factors.(3)The spatial distribution patterns of SOC and TN were similar in four different layers.In general,it increased from west to east and from north to south with an overall plaque-like distribution pattern.These areas of high values were mainly concentrated in Haibei,Guoluo,Yushu,Naqu and Changdu,while these areas of low values were mainly concentrated in Hercynian,Lhasa and Shigatse.(4)The contents of SOC and TN were significant correlation with the annual average temperature.In soil layers above 30 cm,SOC was significant positive correlation with annual precipitation,and there was no correlation in soil layers below 30 cm.However,TN and annual precipitation showed extremely significant positive correlations in different soil layers.Except for the soil layers below 30 cm,there was no correlation between TN and altitude.There were significant negative correlations between SOC and TN and elevation.in other soil layers.The contents of SOC and TN in meadow were greater than that of steppe,and their contents gradually decreased with the increase of soil depth in each grassland type.When the slopes were between 5 and 8°,the contents of SOC and TN were the highest.However,their contents were lowest when slopes were less than 5°.Moreover,the no significant difference was observed when slopes were other.In different aspects,the contents of SOC and TN were shown as cloudy slope > half cloudy slope > half sunny slope > sunny slope.The contents of SOC and TN were negative correlation with bulk density and significant positive correlation with total phosphorus(TP),respectively.Except for the soil layers below 30 cm,there was no correlation between TN and pH,the SOC and TN were negatively correlated with pH in other soil layers.