Research On Water Sources Of Riparian Plants Based On Stable Hydrogen And Oxygen Isotopes In Lanzhou Section Of The Yellow River,China

Riparian vegetation is the basic structure and ecological component of the river.It is an important landscape feature that regulates the ecological process of the river and acts as the interface and ecological zone between the landing site and the river ecosystem.It is more sensitive to changes in the water cycle.For arid and semi-arid areas,the riparian zone can regulate floods,prevent natural disasters,and regulate regional climate,which is of great significance for maintaining biodiversity and ecosystem stability.Tamarix ramosissima,Salix matsudana,Phragmites australis,Ulmus pumila are the dominant riverside plants in Lanzhou section of the Yellow River.They have the advantages of high survival rate,rapid growth and strong adaptability.They not only protect rivers and floods,protect bank slopes,resist wind and soil,and regulate regional climate.It also has the function of beautifying the environment and creating riverside vegetation landscape.At present,there is a lack of research on the source of water for plants on the banks in Lanzhou section of the Yellow River.Therefore,this paper selected three sampling sites along Lanzhou section of the Yellow River,and collected samples of typical plants Tamarix ramosissima,Salix matsudana,Phragmites australis,Ulmus pumila xylems of Lanzhou section of the Yellow River,as well as the potential water sources(precipitation,soil water,river water and groundwater).Using the oxygen isotope direct comparison method,the Bayesian mixture model Mix SIAR and the proportion of similarity index(PS index)to analyze the utilization rate of riparian plants to various potential water sources and the water use relationship between different plants,and to determine the various plants.Correlation between potential water sources and various environmental factors.The results showed that:(1)During the whole sampling period,the?¹⁸O of xylem of Ulmus pumila was the highest,that of Salix mariculata was the lowest,and the?¹⁸O of xylem of Tamarix tamarissima and Phragmites australis were in the middle,which was close.The variation of?¹⁸O in precipitation can be divided into three stages,the variation of?¹⁸O and?²H in precipitation from June to September was relatively slow,while the variation range of?¹⁸O and?²H in precipitation from April to June and September to October was larger.The?¹⁸O and?²H values of river water and groundwater were close to each other,which are basically the smallest,and the monthly changes of river water and groundwater were relatively stable.The isotopic values of soil water in the study area varied with the soil depth.Due to the influence of evaporation,the?¹⁸O and?²H values of shallow soil water were obviously higher than those of middle and deep soil water.(2)Among all water bodies,the?¹⁸O and?²H values of plant water were the closest to those of soil water and river water.The?¹⁸O and?²H of soil water in the whole study area were located between the?¹⁸O and?²H of plant xylem water,precipitation,river water and groundwater,which indicated that soil water was the link between precipitation and plant water.The slope and intercept of the local atmospheric precipitation line and the soil water line equation in the study area were less than those of the global atmospheric water line equation,which indicated that the climate was drier and the evaporation phenomenon was stronger,and the soil water has undergone intense evaporation in the study area.Compared with plant water,the distribution of soil water,river water and groundwater near the local atmospheric precipitation line,it reflected that precipitation in this area had a recharge effect on river water,groundwater and soil water.The mean value of Soil water excess(SW-excess)in plant was negative,which indicated that plant water was more depleted than soil water,and the phenomenon of hydrogen isotope depletion was confirmed.(3)During the entire sampling period,the main water sources of Tamarix ramosissima,Phragmites australis and Ulmus pumila were shallow soil water(0-30cm),and the utilization rates were 33.9%,41.13%and 40.04%,respectively,while the main water source of Salix matsudana was river water,and the utilization rate was 31.2%.The proportion of similarity index(PS index)among riparian plants was basically higher,which showed that Tamarix ramosissima,Salix mariculatum,Phragmites australis and Ulmus pumila had more utilization of the same water source.When the shallow soil water content was high,the utilization ratio of Tamarix ramosissima,Salix artemissima and Phragmus australis to the shallow soil water increased obviously,while when the shallow soil water content decreased,the utilization ratio of the deep soil water and the river water increased.The main water source of Salix mariculata was river water,which is mainly related to the older age of Salix mariculata and the deeper root system.The study area was located in the special geographical location of the floodplain,so plants used all kinds of water uniformly,which was an optimal water absorption mode.However,when the shallow soil moisture was low,the utilization rate of river water will be increased,and the water source will be transformed,so that plants can obtain a more stable water source.