| Studying the water use characteristics of different vegetation in the dunes-meadows of Horqin Sandy Land can provide a scientific reference for local ecological reconstruction and efficient use of water resources.In this thesis,the study objects are the bare land of mobile dunes,semi-mobile dunes,Artemisia halodendron,meadow reeds,and meadow corn.The hydrogen and oxygen isotope technology is used to study the precipitation,groundwater,soil water and plant water of different vegetations in dunes-grassland.The characteristics of hydrogen and oxygen isotope changes,combined with a multivariate linear mixed model,systematically clarify the water use efficiency of different vegetations throughout the growth period,the contribution rate of continuous rainfall drops to soil water at different levels,and the water use efficiency of different vegetations.Main research The results are as follows:（1）Based on the precipitation isotope data collected from April to October in 2020,the precipitation equation line（LMWL）of the study area is obtained:δD=7.85δ18O+18.91（R2=0.934）.TheδD andδ18O values of precipitation ranged from-128.87‰-10.39‰,and theδ18O values of precipitation ranged from-16.70‰-7.67‰.Compared with the global precipitation equation lines,the slope of the precipitation equation line in the study area was smaller,indicating that the precipitation in The Horqin Sandy Land was smaller and evaporation was stronger.Isotope values were relatively enriched in rainy season（June-August）and depleted in dry season（September-October）,showing obvious seasonal variation characteristics of"high in summer and low in winter".（2）The variation range of hydrogen and oxygen isotopes in different water body is as follows:atmospheric precipitation>soil water of Artemisia artemisia>reed soil water>corn soil water>reed soil water>stem water of Artemisia artemisia>reed stem water>corn stem water>semi-mobile dune groundwater>meadow groundwater.The mean values of hydrogen and oxygen isotopes are soil water>atmospheric precipitation>stem water>groundwater.The intercept and slope of soil water evaporation line of semi-mobile dune are larger than those of meadow,indicating that the soil water evaporation of semi-mobile dune is more intense than that of meadow,and the soil water movement of semi-mobile dune is faster than that of meadow,and the evaporative fractionation is more intense.（3）Based on the quantitative analysis of direct comparison method and multiple linear mixed model,the results showed that the shallow and middle-level soil water（0-40cm and 40-80cm）was mainly utilized in May and June,and the utilization rates were 34.40%and 31.60%,respectively.In July and August,the soil water in the middle layer（80-120cm）was mainly used,and the utilization rate was 44.00%and 21.00%,respectively.In September and October,the utilization rate of deep soil water（120-160cm and 160-200cm）was 31.60%and 34.40%,respectively.Meadow phragmites communis mainly utilized shallow soil water of 0～20cm,and the utilization rates were69.70%,37.60%,43.10%,45.20%,64.40%and 76.70%,respectively,from May to October.Only in June,phragmites communis had a higher utilization rate of groundwater,and absorbed a large amount of deep soil water（40～80cm）in July and August.The utilization rates were 44.70%and 41.70%,respectively.For meadow corn,the soil water utilization rate of the same layer in different months was calculated as 23.05%,22.68%,23.28%and 22.18%,respectively.The utilization rate of shallow soil water（0-20 cm）was phragmites australis>maize>Artemisia scoparia.（4）Under the condition of continuous rainfall,the three plants mainly used the shallow and middle soil water after 1 day of rainfall,and the shallow soil water of0-40cm was mainly used by A.chabagaricus,with 27.70%utilization rate.Phragmites australis mainly utilized shallow soil water of 0～10cm,and the utilization rate was42.30%.Maize mainly uses shallow soil water of 0～10cm,and the utilization rate is71.90%.At the same time,there were significant differences in shallow soil moisture content（0-20cm）of Artemisia annua,shallow soil moisture content（0-10cm）and deep soil moisture content（40-80cm）of Phragreed,and no significant differences in soil moisture content among different layers of maize under continuous rainfall conditions.（5）Under the condition of continuous rainfall,theδ18O andδD values of different vegetation belts fluctuated from large to small in the following order:bare land on mobile dune>Artemisia caphaga on semi-mobile dune>maize on meadow land>reed on meadow land.The significant difference between semi-mobile dune and meadow was0～40cm in shallow soil.Different between them is the difference in half mobile sand dunes and artemisia shallow soil water delta D value,the delta 18 o in more before and after 1 day,3 day,5 days there are significant differences,reeds and meadow corn and soil water delta only 18O value only in the more significant differences with the 1 day after the rain,soil water delta D values in the reeds and there is no significant difference between corn.（6）Under continuous rainfall,the contribution rate of rainfall to soil water at all levels decreased gradually with the increase of sampling days.The contribution rate of rainfall in the 1st,3rd and 5th days to surface soil water in 0-80 cm of Artemisia artemisia was 19.45%,14.64%and 11.41%,respectively.The contribution rate of rainfall in the first,third and fifth days after rain to surface soil water in 0-20cm of maize was 15.60%,5.61%and 1.03%,respectively.The contribution rate of rainfall in the 1st,3rd and 5th days to soil water in 0-20cm of phragmites australis was 14.27%,2.03%and 0%,respectively.The contribution rate of rainfall to shallow soil water（0-20cm）in 1,3 and 5days after rain was in the descending order:Artemisia javanica（11.40%-18.01%）>maize（1.03%-15.60%）>reed（2.03%-14.27%）. |
