Study On Plant Water Use Efficiency And Its Influencing Factors In Different Ecosystems Of The Xiangride-Qaidam River Basin

Water resources are one of the important components of natural resources and a key factor for agriculture and ecological environment in arid and semi-arid areas.Located in the southeastern part of the Qaidam Basin,the Xiangride-Qaidam River Basin is the main water source for the agricultural irrigation area of Xiangride Oasis,and the water resources demand is increasing due to the rapid economic development and large number of migrants moving into the area,so it is important to study the water use efficiency of plants in this basin for ecological restoration and water resources regulation in arid areas.Based on this,this study used stable carbon isotope method to study plant leaves of different ecosystems(farmland ecosystem,scrub ecosystem,meadow ecosystem and grassland ecosystem)in the watershed,and adopted a combination of field sampling and indoor analysis to compare the composition characteristics of?¹³C values and water use of different ecosystems,and analyzed the influence of soil and leaf indicators on water use efficiency.The effects of soil and leaf indicators on water use efficiency were analyzed.The results obtained from this study are as follows.(1)Most of the plants in the Xiangride-Qaidam River Basin are C3 plants,and the?¹³C values of the leaves of the dominant species in different ecosystems vary from-14.09 to-30.87‰,and the average value of?¹³C is-26.47‰,which is significantly more positive than the average value of?¹³C of the plants investigated globally,probably because of the low annual precipitation and strong evaporation in the area,and the plants are under obvious When the soil water content and air humidity decrease,the plant leaves will choose to close part of the stomata to reduce the evaporation of water,and the ability of plants to recognize CO₂is reduced,resulting in positive carbon isotope values of leaves.(2)The variability of plant water use efficiency in different ecosystems in the Xiangride-Qaidam River Basin was significant,ranging from 24.39 to 102.51?mol·mol^-1.The water use efficiency of meadow ecosystem was the highest,the water use efficiency of farmland ecosystem was the least variable,and the water use efficiency of scrub ecosystem was the most variable;the variability of plant water use efficiency in the basin The variability of plant water use efficiency in the watershed was moderate to low,with small variability and strong stability.(3)The?¹³C values of plant leaves in the four altitude gradients from 2500 to3000 m,3000 to 3500 m,3500 to 4000 m,and above 4000 m ranged from-14.09 to-29.50‰,-23.47 to-28.15‰,-23.36 to-30.86‰,and-24.81 to-28.92‰,respectively;the plant water use efficiency varied from 24.39 to 81.37?mol·mol^-1,42.52 to 67.57?mol·mol^-1,42.15 to 102.51?mol·mol^-1,47.5 to 74.74?mol·mol^-1,and the rates of change were 233.62%,58.91%,143.54%,and 57.18%.The differences in?¹³C values and water use efficiency of plant leaves on the altitude gradient were not significant.The water use efficiency of agricultural and grassland ecosystems was positively correlated with elevation,and the scrub and meadow ecosystems showed different high value zones of water use efficiency in different habitats at different elevation gradients.(4)The effects of soil indicators on the water use efficiency of different ecosystems were as follows:total phosphorus content was the main factor affecting water use efficiency in farmland ecosystems,total nitrogen content was the main factor affecting water use efficiency in scrub ecosystems,soil water content was the main factor affecting water use efficiency in grassland ecosystems,and soil conductivity was the main factor affecting water use efficiency in meadow ecosystems.(5)The correlation analysis of water use efficiency and leaf indexes showed that water use efficiency was significantly positively correlated with total phosphorus content and negatively correlated with carbon to nitrogen ratio.That is,total phosphorus content and carbon to nitrogen ratio were the main factors affecting water use efficiency on the leaf index.