Research On Water Sources Of Plants In Different Ecosystems In Xiangride-Qaidam River Basin

The Xiangride-Qaidam River Basin,located in the southeast of the Qaidam Basin,is a sensitive area of ecological fragility and global change.The watershed has diverse ecosystems and rich vegetation types,and the water use of plants affects the watershed's hydrological processes and water balance.The study carried out vegetation survey,sample collection and determination of hydrogen and oxygen stable isotopes in seven typical ecosystems of alpine meadow,alpine grassland,alpine shrub,temperate grassland,desert shrub,halophyte meadow and farmland in the basin.On this basis,the vegetation characteristics and soil water content were analyzed,and the hydrogen and oxygen stable isotope composition characteristics of each potential water source(precipitation,soil water,groundwater and river water)were discussed.Finally,combined with the Bayesian mixture model(Mix SIAR),the water sources of plants in different ecosystems in the watershed were quantitatively analyzed,and the water use strategies of watershed plants were further discussed.The main findings are as follows:(1)The ecosystems in the basin are rich in species,and the plant community structure of different ecosystems is different.Among them,the halophyte meadow has the largest vegetation coverage,and the alpine shrub ecosystem has obvious stratification(shrub layer and herb layer);the soil water content of each ecosystem was significantly different(P<0.05),the soil water content of the alpine meadow(26.8±1.8%)was the highest,and the soil water content of the desert shrub(3.8±0.3%)was the lowest;in the vertical direction,the minimum value of soil water content mostly occurs in the 0?10 cm soil layer.(2)The slope and intercept of the Local Meteoric Water Line(LMWL)are both smaller than the Global Meteoric Water Line(GMWL),indicating that the local atmospheric precipitation was strongly affected by secondary evaporation in the air during the sampling period;the?D and?¹⁸O values of groundwater and river water are concentrated and distributed in the lower right of LMWL;the slopes of the Soil Water Line(SWL)of each ecosystem are all smaller than LMWL,indicating that soil moisture in different ecosystems in the watershed undergoes different degrees of evaporation and fractionation,mainly in shallow soils;according to the hydrogen and oxygen stable isotope composition of plant water distributed near SWL,it can be judged that plants mainly absorb and utilize soil water,and the values of?D and?¹⁸O of plant water are significantly different(P<0.05)among the ecosystems.(3)The water use strategies of plants in various ecosystems in the watershed were significantly different.Plants in alpine meadows mainly use 0?10 cm soil moisture except Blysmus compressus;the main water absorption layer of alpine steppe plants is distributed in all soil layers except 40?60 cm;Myricaria squamosa and Achnatherum splendens of alpine shrubs mainly use river water,and other plants mainly use 0?20 cm soil water;the main water sources of the dominant species of Achnatherum splendens grassland(Achnatherum splendens,Kalidium foliatum,Reaumuria kaschgarica and Salsola laricifolia)are three different soil layers;in the desert shrub ecosystem,Nitraria tangutorum and Haloxylon ammodendron mainly use groundwater,and the main water absorption levels of other plants do not overlap with each other;The plants in the halophytic meadow ecosystem may mainly absorb and utilize the water and groundwater in the 40?100 cm soil layer due to salt stress;in the farmland,Triticum aestivum mainly absorbs and utilizes groundwater through its developed root system during the sampling period,while the root system of Solanum tuberosum is mainly distributed in the surface soil,so it mainly absorbs and utilizes 0?10 cm soil water,and the rest of the crops absorb the water sources relatively uniformly.To sum up,in the case of good soil moisture conditions,plants have less competition pressure for water,and more surface soil water is absorbed and utilized.When the water conditions are not good,plants will use different water sources to avoid direct competition for water.(4)Through analysis and discussion,it is found that some plants have flexible water use strategies,and their water absorption strategies are also different in different habitats;water conditions,altitude,changes in the groundwater table,and soil salinity stress can also affect the water source of plants.