Variation Of Soil Organic Carbon And Its Relationship With Soil Factors In Subalpine Shrubland In The Eastern Qilian Mountains

Soil organic carbon pool is an important part of the global carbon cycle,and the accumulation and decomposition affect the balance of the global carbon cycle.As an important ecological barrier in Northwest China,the Qilian Mountains has complex natural environment and obvious vertical zonality of soil and vegetation types.Scientific understanding of spatial and temporal differentiation of soil organic carbon and its relationship with soil factors in subalpine shrubland of the eastern Qilian Mountains is of great significance for further understanding of soil organic carbon accumulation and decomposition in alpine mountainous areas.Selecting the vegetation growth period from May to October 2019,two sample plots,semi-shady slope and semi-sunny slope,are set up in subalpine shrubland in the eastern Qilian Mountains.A total of 560 soil samples were collected in the study area,and the spatial and temporal variation characteristics of soil organic carbon and soil factors were studied by classical statistical methods,Pearson correlation analysis,unitary linear regression,principal component analysis and multiple linear regression,in order to provide theoretical basis for regional ecological carbon cycle and ecological environment construction.The main results are as follows:（1）The content of soil organic carbon at the semi-shady slope and the semi-sunny slope is significantly different in soil layer depth of 0-10 cm（p<0.05）.On the time scale,the content of soil organic carbon in May and June is semi-sunny slope>semi-shady slope,and it is semi-shady slope>semi-sunny slope from July to October.The comtent of soil organic carbon decreases with the soil layer depth,but it shows semi-sunny slope>semi-shady slope in soil layer depth of 0-40cm,and it shows semi-shady slope>semi-sunny slope in soil layer depth of 40-60 cm,which reflects that the content of soil organic carbon in the same soil layer depth is affected by slope aspect.（2）The spatial and temporal changes of four soil factors in the study area are different.The content changes of soil water,soil available nitrogen and soil organic carbon are consistent,that is semi-sunny slope>semi-shady slope in May and June,and that is semi-shady slope>semi-sunny slope from July to October.The content of soil available phosphorus in July and October is semi-sunny slope>semi-shady slope,and it is semi-shady slope>semi-sunny slope from May to June and from August to September.The content of soil available potassium is semi-shady slope>semi-sunny slope from May to October.The content of soil water at different aspect decreases gradually with the soil layer depth.The content of soil nutrient in the surface layer is higher than that in deep layer,but the difference is significant with the soil layer depth.（3）Linear regression analysis of soil organic carbon and soil factors,with 20cm soil layer depth at different slope directions in the study area,shows that there is a significant positive correlation between soil water and soil organic carbon（p<0.01）.The correlation between soil available nutrients（N,P,K）and soil organic carbon is different.The soil available nitrogen and soil organic carbon in soil layer depth of 20-40 cm at the semi-sunny slope have significant negative correlation（p<0.01）,but they have significant positive correlation in other soil layer depths which is consistent with the whole soil profile of semi-shady slope（p<0.01）.Except for soil layer depth of 0-20 cm,soil available phosphorus and soil organic carbon at the semi-shady slope and the semi-sunny slope show significant positive correlation（p<0.01）.There is a significant negative correlation between soil available potassium and soil organic carbon in soil layer depth of 40-60 cm（p<0.01）,and there is a positive correlation between soil available potassium and soil organic carbon in other soil layer depths（p<0.01）.（4）Principal component analysis of soil factors affecting the content change of soil organic carbon in different slope directions and depths was calculated.The content change of 70.252%of soil organic carbon at the semi-shady slope is affected by soil water content,soil available nitrogen and soil available phosphorus,while that of53.988%of soil organic carbon at the semi-sunny slope is affected by them.At the soil layer depth of 20-40 cm at the semi-sunny slope,the cumulative explanations of four soil factors for the content change of soil organic carbon reaches 90.853%.（5）Linear regression analysis of soil organic carbon and soil factors in the study area was calculated.The regression equation of the semi-shady slope is y=0.775x₁+0.185x₂-0.277x₃+0.081x₄+5.471,and that of the semi-sunny slope is y=0.364x₁+0.081x₂+0.258x₃+0.089x₄+25.829,and R² is 0.809 and 0.527 respectively.