Study On Water Utilization Characteristics Of Different Types Of Sand-fixation Shrubs In The Hobq Desert Based On Stable Isotope Techniques

For a long time,planting artificial vegetation is the most effective way to reduce wind and sand hazards and improve the ecological environment in sandy areas.However,vegetation construction activities that focus too much on the short-term ecological benefits of the wind and sand fixation vegetation system have led to different degrees of degradation and even death of the existing wind and sand fixation vegetation system after a certain period of recovery,which seriously threatens the national ecological security and sustainable development of the region.The lack of understanding of the water use characteristics of sand-fixing plants and the lack of effective guidance for practice are important reasons for the above phenomenon.In this study,different types of typical sand-fixing plants were selected from the Kubuqi Desert,where artificial sand-fixing plants are well developed,including Caragana korshinskii,Salix psammophila,Artemisia ordosica,and Sabina vulgaris.The sources and proportions of water used by sand-fixing plants,their water absorption depth and their response to precipitation changes were studied.The study aimed to understand the characteristics of water utilization of sand-fixing plants and explore the optimal allocation techniques of different types of sand-fixing plants.Furthermore,it is committed to exploring the strategies of sand-fixing plants to adapt to the drought environment and provide relevant references for improving the quality and stability of damaged ecosystems.The main results of the study are as follows.(1)In the early stage of the growing season(June),the soil moisture content of different types of sand-fixing vegetation restoration areas showed the highest in the Sabina vulgaris sample site,followed by the Artemisia ordosica sample site,and comparable in the Salix psammophila and Caragana korshinskii sample sites.With the increase in precipitation,the soil moisture content of different types of sand-fixing vegetation restoration areas increased,and the soil moisture content of the shallow and middle layers(0?40 cm and 40?80 cm)showed higher characteristics than that of the deep layers.The recharge effect of different amounts of rainfall on soil moisture content varied.The recharge effect of small rainfall(4.8 mm)events on the soil moisture content of Salix psammophila and Caragana korshinskii was not obvious,while the recharge effect on the 0?40 cm surface soil of Artemisia ordosica and Sabina vulgaris was more obvious.With the increase in rainfall,the recharge effect of precipitation on soil moisture was enhanced,but the recharge effect on soil moisture in the deep layer(100?140 cm)was limited.(2)From June to September,soil water hydrogen isotope values differed greatly between different types of sand-fixing vegetation restoration areas.The soil water-hydrogen isotope values in the Sabina vulgaris sample site were lower than those in other sample sites,and the soil water-hydrogen isotope values in each site tended to be stable with the increase in soil layer.The differences in hydrogen isotope values between different types of sand-fixing vegetation in response to changes in precipitation may be due to different rainfall intensities and evaporation rates of soil water.Hydrogen isotope values of xylem of the same species of sand-fixing vegetation varied significantly from June to September,with the largest differences in hydrogen isotope values of Artemisia ordosica and the smallest differences in hydrogen isotope contents of Caragana korshinskii.The response of water hydrogen isotope values of different types of sand-fixing plants to changes in precipitation varied.Among them,the hydrogen isotope values of the xylem of Artemisia ordosica responded most significantly to small precipitation events,and the hydrogen isotope values of the xylem of Sabina vulgaris responded most significantly to moderate rainfall events.(3)In June,when the soil moisture content was low,Caragana korshinskii and Salix psammophila mainly used soil water below 60 cm,even using groundwater.Sabina vulgaris utilized both shallow and deep soil water.Artemisia ordosica mainly utilized soil water in the 0?40 cm layer.In August and September,Caragana korshinskii and Salix psammophila mainly used deep soil water.Artemisia ordosica mainly used soil water in the 0?60 cm layer,and Sabina vulgaris had a relatively balanced source of water use.Under the small rainfall event(4.8 mm),there was no significant change in the depth of water used by different types of sand-fixing plants.Under larger rainfall(22.4 mm),Caragana korshinskii and Salix psammophila still mainly used deep soil moisture,while the depth of water use of Artemisia ordosica and Sabina vulgaris became shallow.(4)From June to September,when the soil moisture content was low,the percentage of soil moisture utilization was as high as 97% in the 0?40cm layer for Artemisia ordosica,53% in the 0?20 cm layer for Sabina vulgaris,and about 60% in the 80?140 cm layer for Caragana korshinskii and Salix psammophila.Under smaller rainfall conditions,the sand-fixing plant Sabina vulgaris mainly utilized surface soil water.With the increase in rainfall,Caragana korshinskii and Salix psammophila also increased the proportion of utilization of soil water in the shallow and middle layers,and gradually increased the proportion of utilization of soil water and groundwater in the deep layer(100?140 cm).(5)When the soil moisture content was low(June),the main absorption depths of Caragana korshinskii and Salix psammophila were80?140 cm,while the main absorption depths of Artemisia ordosica and Sabina vulgaris were 0?40 cm.As the soil moisture content improved(September),the average absorption depths of the four sand-fixing plants did not change much.Different types of sand-fixing plants responded differently to different magnitudes of precipitation changes in their average water absorption depths.The overall response to small rainfall events was limited,while the response to larger rainfall events was more pronounced.Based on the above results,Caragana korshinskii and Salix psammophila mainly utilized soil water in the 40?80 cm and 80?140 cm layers.Salix psammophila utilized a larger proportion of groundwater,while Artemisia ordosica and Sabina vulgaris mainly utilized soil moisture in the 0?40 cm layer.Therefore,the combination of sand-fixing plants,Artemisia ordosica and Sabina vulgaris,will increase the water competition between artificial sand-fixing vegetation,while the combination of both with Caragana korshinskii and Salix psammophila will avoid the water competition between artificial sand-fixing vegetation to a certain extent.