The Characteristics Of Plants Water Stable Isotopic And The Depth Of Water Uptake Of Common Plants In Lanzhou City

Water is a necessary condition for the growth of plants,which always affects the quantity and distribution of plants.Especially in arid and semi-arid areas,water is the main factor that restricts the growth of plants and the primary productivity.Studying the depth of water absorption in plants helps to understand how well plants adapt to different environments.Urban greening is an indispensable part of urban construction in Lanzhou City,and it's also an indicator of whether the city has vitality.Urban greening plays an irreplaceable role in improving the ecological environment and improving the quality of the environment.At present,there are few studies on the basic characteristics of plant isotopes and how to deal with the different water conditions in Lanzhou.Therefore,it is necessary to study the characteristics of the stable hydrogen and oxygen isotopes of leaf water and xylem water in common plants and to explore the water use strategies for typical plants in different seasons.Selecting common species of Platycladus orientalis,Sophora japonica,Salix babylonica,Euonymus japonicas,Forsythia suspense,Rosa xanthina Lindl,and Caragana korshinskii in Lanzhou as the research object,this study systematically discussed the water use strategy of Platycladus orientalis,Sophora japonica,Salix babylonica,Rosa xanthina Lindl and Caragana korshinskii.And we conducted a field survey on the characteristics of vegetation,soil and hydrology.Through the analysis of the characteristic of xylem water in plant and soil water,this paper analyzed the main water uptake area and contribution rate of plants by the direct viewing method and multiple linear mixed model.The main results were showed that:?1?From the study of daily variation of stable isotope of plants in Northwest Normal University,the changing range of?¹⁸O in 2015 is greater than that in 2016.The value of?¹⁸O in deciduous plants is richer and it has greater variation than that in evergreen plants.The value of?¹⁸O in Platycladus orientalis leaf water presents a rising trend in No.2 sampling points on July 28,2016.The highest value of?¹⁸O is monitored at 18:00.The value of?¹⁸O in Caragana korshinskii leaf water has a large fluctuation and the value of?¹⁸O increases rapidly from 10:00 to 13:00.The value of?¹⁸O in Platycladus orientalis xylem water and Caragana korshinskii xylem water almost has no change,indicating that the origin water has no obvious change.The value of?¹⁸O in Agropyron cristatum water increases from 08:00,and reaches the highest value in 16:00,and then declines.?2?We collected 7 times in No.1 sampling points of northern mountains,and the value of?¹⁸O in Platycladus orientali leaf water and Caragana korshinskii leaf water presents a fluctuated variation.The changing range of Caragana korshinskii leaf water was larger than that of Platycladus orientalis leaf water and that indicates Caragana korshinskii is more sensitive to the environment.The value of d in Caragana korshinskii leaf water is depleted as time go on and the negative degree is getting smaller and smaller,stating that transpiration gradually slow down.The value of?¹⁸O in Salix babylonica leaf water declines before July 23,2016 and then the value present an upward trend,but the corresponding d is on the rise.The value of?¹⁸O in Salix babylonica xylem water changes slowly,only in the range of-8.4‰^-7.0‰.The value of?¹⁸O Sophora japonica leaf water shows a fluctuating variation,and the change ranges lager than xylem water.Rosa xanthina Lindl is a common green plant in Lanzhou,and the value of?¹⁸O has no significant change in other months except for the first sampling.?3?In Beishan Mountaions No.1 sampling points,0³0 cm soil water content change is more complex than deeper soil water,because the shallow soil is more easily influenced by the external environment.Compared with the value of?¹⁸O in shallow and deep soil water,it can be found that the value of?¹⁸O in shallow soil water is richer than that in deep layer.The change of soil surface water content in the Zhixing College of Northwest Normal University sampling site is significantly higher than that in deep layer and the value of soil water content was higher than No.1 sampling points of northern mountains.The average value of?¹⁸O in each layer of soil water presents a trend:?¹⁸O0¹0cm>?¹⁸O10³0cm>?¹⁸O30⁵0cm>?¹⁸O50⁷0cm>?¹⁸O70¹00cm.?4?Compared the characteristics of oxygen isotope of xylem water?Platycladus orientalis and Caragana korshinskii?with soil water,We find that the two plants mainly absorb shallow soil water.We used IsoSource multi linear mixed model to determine the contribution rate in each layer of Platycladus orientalis and Caragana korshinskii.The contribution of soil water is on the maximum rate of Platycladus orientalis at May5,July 23,September 3,September 23 and October 17.Caragana korshinskii mainly absorbs shallow soil water at depth 0¹0 cm and 10³0 cm in each month of 2016.?5?Compared the value of?¹⁸O of xylem water?Salix babylonica,Sophora japonica and Caragana korshinskii?with soil water,We find that the three kinds of plants absorb deep soil water.Salix babylonica mainly absorbs 70¹00 cm soil water at April 30,May 27,July 23 and October 18,while the contribution rate of each layer soil water is similar in the other months.The absorbed rate of Sophora japonica is similar at September 23 and mainly absorbs 70¹00 cm soil water in other month.Plants tend to absorb deeper soil water where the Rosa xanthina Lindl has low soil water content.