Water Use Strategies For Typical Plants In The East Sandy Land Of The Yellow River In Ningxia Under Different Rainfall Conditions

As a major regulator in the water cycle of the Soil-Plant-Atmosphere-Continuum system.Caragana korshinskii and Elaeagnus angustifolia were excellent tree species for wind breaking and soil conservation in arid regions,but their water use strategies and water use relationships in the context of global climate change were unclear.Therefore,it was important to study the water use strategies and water use relationships of typical artificial sand-fixing plants in order to evaluate the sustainable development of artificial ecosystems in arid sand areas.We took the typical artificial sand-fixing plants,Ck and Ea,in the east sandy land of the Yellow River in Ningxia as the research objects,and utilized the backward trajectory model,trajectory cluster analysis,potential source contribution function and concentration-weighted trajectory to quantitatively reveal the time-scale effects of precipitation stable isotope composition and water vapor sources in the study area.The hydrogen-oxygen stable isotope technique,direct comparison method,bayesian mixture model and similarity proportion index were used to analyze the differences in water use strategies of Ck and Ea under different magnitude of precipitation events and the water use relationship between them.The results showed that:(1)The hydrogen-oxygen stable isotope composition of precipitation in the east sandy land of the Yellow River in Ningxia has obvious seasonal variations,with a clear bias towards summer than spring and autumn;while the d-excess in precipitation shows the opposite seasonal variation,with a clear bias towards autumn than spring and summer.The slope and intercept of the local meteoric water line(LMWL)were smaller than that of the global meteoric water line(GMWL)during the study period,reflecting that the study area was influenced by a stronger secondary evaporation effect under clouds.The LMWL differs significantly at seasonal scales,with the slope and intercept of the spring LMWL being lower than those of the growing season and the slope and intercept of the autumn LMWL,except in summer,indicating that precipitation in the study area was more strongly influenced by secondary evaporation under clouds in summer,followed by spring.The temperature effect of δ18O composition in precipitation was significant during the study period,but the precipitation effect was not significant.Backward trajectory clustering,PSCF and CWT analyses indicated that precipitation water vapour in the study area was significantly influenced by westerly water vapour,as well as by local recirculation water vapour recharge and Arctic Ocean water vapour.In spring,the potential evaporation source areas of water vapour were mainly distributed in the peripheral areas of the study area;in summer,mainly in the western and southern parts of the study area;and in autumn,mainly in the southern and southwestern parts of the study area.(2)Except for heavy rainfall,the main source of water for both plants was the same after light and moderate rainfall.After light rainfall,both lemon and jujube relied mainly on deep soil water;after medium rainfall,both Ck and Ea shifted to mainly using shallow soil water;after heavy rainfall,the main source of water for Ck shifted to deep soil water,while Ea still mainly used shallow soil water,indicating that both Ck and Ea adopted a resource-dependent water use strategy,and that the two species spatially used soil water at different soil depths,promoting coexistence between them through the This indicated that both Ck and Ea species adopt a resource-dependent water use strategy and spatially use soil water at different soil depths,promoting coexistence between them through ecological niche differentiation in soil water use.In the vertical direction,the fine root biomass of Ck and Ea was higher in the 60-80 cm and 40-60 cm soil layers than in other soil layers,respectively,and the root length density,root surface area density and root bulk density of the fine roots of both species showed an overall trend of increasing and then decreasing with increasing soil depth.In the horizontal direction,the root length density of the fine roots of Ck and Ea showed an increasing trend,reaching the maximum value at 0.5-1 m.The root surface area density of the fine roots showed that Ea>Ck at both horizontal distances,and the root volume density of the fine roots showed that Ck>Ea at 0-0.5 m;while at 0.5-1.0 m it showed that Ea>Ck,and the root volume density showed a decreasing trend with increasing horizontal distance.The root volume density generally decreased with increasing horizontal distance,and the fine root biomass of Ck sticks was the largest at both horizontal distances.The distribution characteristics of the fine roots of the two species determine their water use strategies,and together with soil moisture content and root functional type,determine the response of the plants to different rainfall events.(3)The PS indices of the two tree species were significantly greater after moderate rainfall than after light and heavy rainfall,indicating that Ck and Ea utilized the same water source more.The PS indices of 92.0%and 91.3%for light and heavy rainfall,respectively,indicated that there was a strong competition for water between the two species,but after light rainfall,Ck and Ea competed more for the same source of water than after heavy rainfall.Except for heavy rainfall,Ck and Ea had the same water use strategy after different amounts of rainfall.After heavy rainfall,the water use strategies of Ck and Ea were different,which was conducive to the stability of the plantation community and the coexistence between the two tree species.