Study On The Root Distribution And Water Source Of Typical Sand Fixing Plants In Xiliugou Basin

The ecological protection and high-quality development of the Yellow River basin is a key strategy in China,and the prevention and control of soil erosion in the ten major holes of the Yellow River in Inner Mongolia is one of the most important tasks.Therefore,in this study,Xiliugou（through the Kubuqi Desert section）,one of the ten major hole-tunnels of the Yellow River,was selected as the study area.We analyzed the root morphology and soil water variation characteristics of three typical sand-fixing plants,clarified the spatial distribution differences of the root systems of three typical sand-fixing plants and the correlation between root biomass and soil water,and analyzed the hydrogen and oxygen stable isotopeδof precipitation,river water,soil water and plant xylem water in the study area.The study area was characterized by the variation of hydrogen and oxygen stable isotopesδD andδ¹⁸O in precipitation,river water,soil water and plant xylem water,and clarified the characteristics of hydrogen and oxygen isotope composition of different water sources and their interrelationships.The Mix SIAR model was applied to quantify the contribution of soil water at different depths to the water utilization of three sand-fixing plants,and to reveal the water sources,water absorption depth and competition for soil water at different depths of three sand-fixing plants in different habitats and different months.This study was conducted to investigate the adaptation strategies of plants to the drought environment under the condition that water is the main limiting factor for plant growth,to enhance the understanding of the root systems and water sources of typical sand-fixing plants,and to provide some reference basis for soil and water conservation and sand control in the Yellow River basin.The main research findings are as follows:（1）The root biomass of lemongrass brome,northern salix and black sagebrush in the study area was 175.77 g,291.18 g and 83.95 g,respectively,and 90%of the root biomass of the three sand-fixing plants was mainly distributed in 0-90 cm,0-50 cm and 0-30 cm soil depth.The fine root biomass of the three sand-fixing plants was 19.06g,37.79g and5.03g,respectively,and the fine roots were mainly distributed in the top soil layer,and the accumulation percentage of fine root biomass showed an exponential decreasing trend with increasing soil depth,and the accumulation percentage of fine root biomass of the three plants could reach 70%-85%in the 0-40cm soil layer.Among the three sand-fixing plants,the fine root attenuation coefficient was the largest in lemongrass,the fine root ratio root length was the largest in black sagebrush,and the fine root length was more average in northern sagebrush.The mean values of soil moisture of the three sand-fixing plants during the study period were in the following order:lemongrass mallow>northern sand willow>black sand artemisia,and the soil moisture of the plants was significantly and positively correlated with the fine root biomass of each plant（P<0.05）.（2）The mean values of soil water content in river terrace and riverbank were 5.1%and 1.9%,respectively,and the soil water content in each layer of river terrace was larger than that in riverbank sample.The mean values ofδD andδ¹⁸O of river terrace and riverbank soil water were-69.69‰,-8.7‰and-59.94‰,-6.8‰,respectively,and the isotopic values of both were significantly different（P<0.05）.The meanδ¹⁸O values of river water and atmospheric precipitation were-8.37‰and-6.04‰,respectively.Theδ¹⁸O of soil water in river terrace was closer to river water,while theδ¹⁸O of soil water in riparian land was closer to atmospheric precipitation,and it could be judged that soil water in river terrace mainly originated from river water and soil water in riparian land mainly originated from atmospheric precipitation.（3）The contribution of river water,atmospheric precipitation and soil water to the plant water of lemon mallow,northern salix and black salix was quantified using Mix SIAR model,and the results showed that the contribution of soil water to plant water was the highest,and the mean contribution was 46.52%,39.2%and 49.77%,respectively.The roots of Lime straw mallow,Northern Salix and Artemisia nigra absorbed more soil water in the 0-30 cm soil layer compared with other layers,with mean values of utilization rate of 26.28%,23.6%and 24.89%,respectively.The root systems of Lemon twig and Northern Salix were more likely to absorb soil water in the 0-30 cm soil layer under better moisture conditions,and the root systems absorbed water in deeper soil layers under poorer moisture conditions,and the sources of water were more balanced,while the root systems of Artemisia nigra absorbed water in a way that the water uptake rate decreased gradually with increasing soil depth.The mean values of PS indices of lemon mallow,northern salix and black salix were all higher than 90%,indicating that the water uptake patterns of lemon mallow,northern salix and black salix were similar,probably due to the fact that the study area was adjacent to the Xiliugou River,where soil moisture was more abundant resulting in more uniform utilization of each water source by plants.