The Root Distribution Characteristics And Water Sources Of Typical Shrubs In Water-Wind Erosion Crisscross Region

This study took the Liudaogou small watershed in Water-Wind Erosion Crisscross Region.Typical sandy shrubs,Caragana korshinskii and Salix psammophila were selected as the research objects in the study area.To clarify the differences of root distribution in arid and semi-arid environments,we collected plant roots,and the root morphology characteristics of the two shrubs at different soil depths were analyzed.The values ofδ¹⁸O andδD from xylem water,soil water and precipitation in the study area were measured,and their constituent characteristics and their correlation were analyzed.Direct comparison method and SIAR model were used to quantify the contribution rate of soil water to plants in each soil layer,and to explore the main water absorption depth,water source and competition of the two plants for soil water at different soil depths in different sampling dates.The further research results indicate that:（1）The fine roots of Caragana korshinskii were mainly distributed below the depth of the 30 cm soil layer in the range of 0～100 cm depth.The root weight density and root length density showed the same trend with the increase of soil depth,but the specific root length and root specific surface area showed the same trend.The fine roots of Salix psammophila were mainly distributed in the soil layer of 0～30 cm.The root density and root length density decreased firsty and then increased with the change of soil depth,and the specific root length and root specific surface area were distributed in wave pattern.（2）The Local Meteoric Water Line equation wasδD=7.69δ¹⁸O+6.14（R²=0.96）,with smaller slope and intercept than the Global Meteoric Water Line.From May to September in2018,the monthly d-excess value is less than the global average of 10‰,in which the three months of may,July and September are positive,and the two months of June and August are negative.The slope and intercept of the soil water line(SWL:δD=5.71δ¹⁸O-15.61,R²=0.87)were significantly lower than the Local Meteoric Line.The slope and intercept of xylem water line of Caragana korshinskii(δD=7.57δ¹⁸O-9.30,R²=0.87)were between the Local Meteoric Line and the soil water line.The slope and intercept of the xylem water line of Salix psammophila(δD=2.58δ¹⁸O-52.08,R²=0.60)were lower than the soil water line.（3）In the different sampling dates,the variation trend of theδD andδ¹⁸O values from soil water are similar with the increase of soil depth,and the variation range decreases with the increase of soil depth.TheδD andδ¹⁸O values from soil water in 0～20 cm（shallow layer）soil layer are more enriched than those in 20～300 cm（shallow layer）soil layer.TheδD andδ¹⁸O values in the soil layer of 0～20 cm（shallow layer）showed obvious seasonal differences,which were enriched in May and June,depleted in July,and then enriched in August and September.（4）In the early period of plant growth（May and June）,the relative absorption ratio of shallow layer（0～30 cm）soil water by Salix psammophila was obviously higher than that by Caragana korshinski,while the absorption ratio of shallow layer（30～60 cm）and middle layer（60～140 cm）soil water by Caragana korshinskii was higher than that by Salix psammophila.In July and August,the relative absorption ratio of Caragana korshinskii and Salix psammophila to soil water in different soil layers was not obviously different.In September,the relative absorption ratio of shallow layer（0～30 cm）and medium shallow layer（30～60cm）soil water of Salix psammophila was slightly higher than that of Caragana korshinskii,while the absorption ratio of middle layer（60～140 cm）and deep layer（140～300 cm）soil water of Caragana korshinskii was slightly higher than that of Salix psammophila.