Study On Sources Of Water For Typical Sand-fixing Vegetation In Horqin Sandy Land

As a major limiting factor for vegetation growth in Horqin Sandy Land,soil moisture determines the carrying capacity for vegetation.Stable isotope technique is a robust tool to track the water sources of vegetation.Related results can provide scientific evidences for water transport paths in the system of soil-plant-atmosphere continuum(SPAC)and for desertification control in this area.To resolve the issue of difficulties in abstracting water from soils of Horqin Sandy Land,this study explored the feasibility of diluting the soil water samples with water of known abundance of stable hydrogen(D)and oxygen(18O)isotopes by employing end-member mixing model(IsoSource model).Using oxygen stable isotope techniques,this study quantified the effects of changing precipitation on soil water uptake strategy of typical vegetation(i.e.,Caragana microphylla and Artemisia halodendron)in this region.We further investigated the responses of root biomass and the root-shoot ratio to the changes in precipitation.The main results are as follows:(1)Method of mixing the soil water abstracted from soils with ultra-pure water can effectively reduce the required volume of soil water when measuring its stable-isotope abundance.Isotope values(?D or ?18O)of soil water,mixing water,and ultra-pure water showed significant linear relationships(R2>0.99,p<0.001).Measured and predicted isotopic data by the End-member mixing model are consistently high with R2>0.99,p<0.001,which was not affected by soil texture and organic carbon content.This work provides a new perspective for measuring stable isotope of soils with extreme low water content in arid and semi-arid areas.(2)The abundance of 18O was significantly higher in the reducing-water treatment than increasing-and control experiment(CK)for both Caragana microphylla and a.halodendron.The results of IsoSource model showed that changes of precipitation significantly changed the water uptake strategy of Caragana microphylla and a.halodendron.For example,Caragana microphylla uptakes soil water from the 0-120 cm profile in May and June for CK and increasing-water treatments.However,soil water in 0-40 cm and 80-120 cm depths were the main sources for reducing-water treatment,accounting for 53.2%,55.3%OF WHAT,respectively.In September,Caragana microphylla mainly uptakes soil moisture from deeper soil layer(100-120 cm)for CK and increasing-water treatment,and across the 40-120 cm soil profile for reducing-water treatment,with percentages of 67.2%,49.6%,94.2%,respectively;Halodendron absorbs soil water uniformly from 0-80 cm soil layers in both June and September for treatments of increasing-water and CK.The contribution of water differed among soil layers for reducing-water treatment,60-80 cm and 20-80 cm accounting for 82.4%and 88.6%of root water uptake for June and September,respectively.(3)Increasing precipitation can significantly increase the root-shoot ratio of Caragana microphylla,which is beneficial to increase its drought resistance.The aboveground biomass of Chabagako decreased significantly with the decrease in precipitation.Significant positive relationships between the root biomass in 0-60 cm and the precipitation were observed in this area for both of the two vegetation types.The root tended to distribute in shallow soil layers when precipitation further decreased in the study area.