Study On Water Use Of Robinia Pseudoacacia And Euonymus Bungeanus In The East Sandy Land Of The Yellow River In Ningxia

Water is a crucial factor limiting artificial vegetation growth in arid and semi-arid regions.Water availability and plant utilization strategy reflect ecosystem response to environmental water conditions,and their changes depend on global climatic variation.The study of plant water use could provide scientific basis for restoration regional vegetation and stand structure optimization allocation of shelter forest.In this study,the typical artificial forest species of Robinia pseudoacacia and Euonymus bungeanus in the east sandy land of the Yellow River in Ningxia were studied.This study was quantified the water consumption of two species in the mixed type during different periods of the growing season,and identified the main factors affecting water consumption in Robinia pseudoacacia and Euonymus bungeanus.Quantified the water source of water consumption for two plants in the mixed plantation,and revealed the water use relationship of Robinia pseudoacacia and Euonymus bungeanus,and elucidated the influence of the Robinia pseudoacacia and Euonymus bungeanus mixed forest model on the soil moisture environment in the region.The results showed that:(1)During the growing season,the diurnal variation of sap flow rates of Robinia pseudoacacia and Euonymus bungeanus showed a trend of increasing first and then decreasing.The start-up time,peak time and minimum time of sap flow of the two species were various in different periods of the growing season.There was a weak nighttime sap flow in Robinia pseudoacacia and Euonymus bungeanus in every month.The water consumption of Robinia pseudoacacia and Euonymus bungeanus were higher in the middle growing season,but lower in the early and late growing season.The water consumption of Robinia pseudoacacia was 1.52 times larger than Euonymus bungeanus.(2)The main environmental factors affecting water consumption of Robinia pseudoacacia and Euonymus bungeanus were vapour pressure deficit,solar radiation,0—40 cm and 40—120 cm gravimetric soil water content.Among the plant leaf attributes,the contribution rate of leaf water retention capability of the two plants was higher.The results of the structural equation model showed that the ten factors explained 89.4%and 87.8%of the time variability of Robinia pseudoacacia and Euonymus bungeanus,respectively.On the one hand,air temperature,solar radiation and vapour pressure deficit was directly affected the water consumption of Robinia pseudoacacia and Euonymus bungeanus.On the other hand,these factors indirectly affected the water consumption of the two tree species by affecting leaf water retention capability,specific leaf area and leaf water content.On the one hand,precipitation directly affected the water consumption of Robinia pseudoacacia and Euonymus bungeanus.On the other hand,it indirectly affected the water consumption of the two tree species by affecting leaf water retention capability,specific leaf area,leaf water content and 0-40 cm gravimetric soil water content.(3)The local meteoric water line in the study area with a slope and intercept lower than that of the global and Chinese meteoric water line,indicating the impact of precipitation evaporation on isotope fractionation.The soil water line in the study area with a slope and intercept of soil water line in plantation were below the local meteoric water line,indicating that the soil water was affected by secondary evaporation.The distribution of hydrogen and oxygen stable isotopes in groundwater was relatively concentrated,mainly distributed between the local meteoric water line and the soil water line.Therefore,groundwater in the study area was supplemented by precipitation and soil water,and groundwater will also supplement soil water to a certain extent.(4)Robinia pseudoacacia mainly used the middle layer soil water and Euonymus bungeanus mainly used the shallow layer soil water in the season with high water consumption.While the shallow layer soil water and the middle layer soil water were ultilized by Robinia pseudoacacia and Euonymus bungeanus separately in the season with lower tree water consumption.In addition,Robinia pseudoacacia and Euonymus bungeanus was able to deal with drought and maintain their own water consumption mainly through the spatial difference of water use strategy under drought seasons.In the seasons when gravimetric soil water content was higher,the water niche overlap degree of Robinia pseudoacacia and Euonymus bungeanus was the highest,and there was a strong water competition relationship.Soil water content was the main factor affecting the water source of plants.Soil nutrients affect the water source of plants by coupling with water.(5)The water use of Robinia pseudoacacia and Euonymus bungeanus might lead the middle and deep soil water deficit.The higher of shallow layer gravimetric soil water content might reflect a trade-off between water and nutrient requirements of plants under the effect of soil water redistribution by plant roots in the sandy land.