Study On Eco-hydrological Process Of Windbreak And Sand Fixation Forest In East Sandy Land Of Yellow River,Ningxia

Conducting research on ecohydrological processes in sandy areas,which was important for ecological restoration and healthy and sustainable development of the environment in arid and semi-arid zones.In this study,Robinia pseudoacacia、Euonymus maackii and Elaeagnus angustifolia forest in the east sandy land of Yellow River were used as research objects.Seasonal characteristics and patterns of transpiration,soil evapotranspiration,soil infiltration,canopy retention and water holding capacity of litter in the growing season（May-October 2019）were analyzed;the microclimate and soil environmental variables were monitored simultaneously.The water transport processes and their influencing factors in sandy woodland ecosystems were elucidated.We clarified the water cycle and ecohydrological effects of different forest ecosystems,which could provide scientific reference for regional water resource regulation and vegetation restoration and reconstruction.The main research results were as follows:（1）The moisture content and mechanical composition of soils in the study area were observed and analyzed,and the soil moisture distribution in the three woodlands exhibited a high degree of spatial heterogeneity.The 60 cm and 90 cm soil layers were the mutation layers of elevated soil moisture in Robinia pseudoacacia and Elaeagnus angustifolia stands,respectively;the 30 cm soil layer in Euonymus maackii stand was the mutation layer of reduced soil moisture.The soils of each stand were mainly loamy sandy loam and sandy loam,and the average distribution of soil fractal dimension of each layer in each stand ranged from 1.49 to 2.74.（2）The transpiration water consumption of Robinia pseudoacacia was the highest（33.59mm）throughout the growing season,followed by Euonymus maackii（20.70mm）and Elaeagnus angustifolia（11.50mm）.The transpiration water consumption of both Robinia pseudoacacia Euonymus maackii showed the highest in July and the lowest in October.The transpiration water consumption of Elaeagnus angustifolia was highest in May,second highest in July and lowest in October.Solar radiation,temperature,relative humidity,vapor pressure deficit and wind speed were all important drivers of water consumption by transpiration in forest trees.The soil evaporation showed that Elaeagnus angustifolia（175.43mm）>Euonymus maackii（166.17mm）>Robinia pseudoacacia（158.51mm）,and overall showed the highest in June and July and the lowest in September and October.Soil water content,solar radiation and air humidity significantly affected soil evaporation（P<0.01）,and soil particle size had an effect on soil evaporation.（3）The distributions of infiltration coefficients of different soil layers in each stand ranged from 0.13 to 2.59.The infiltration coefficient,the average infiltration rate and the accumulated infiltration amount were the highest in the Elaeagnus angustifolia forest,which showed the strongest soil infiltration capacity,followed by the Robinia pseudoacacia and Euonymus maackii forests.The total porosity of the soil was the main influencing factor on the initial infiltration rate,and the capillary porosity,capillary water holding capacity,saturated water holding capacity and sand content had some influence on the initial infiltration.The capillary water holding capacity and sand content had an effect on the steady infiltration rate.The relationship of soil infiltration rate with infiltration time could be expressed as a power function for all forest sites（R²>0.77）.（4）The canopy interception rate during the whole growing season was Robinia pseudoacacia（11.36%）>Elaeagnus angustifolia（8.14%）>Euonymus maackii（5.55%）.Three stands exhibited understory penetration rainfall>interception>trunk flow,and penetration rainfall,interception and trunk flow showed a linear increasing relationship with precipitation（R²>0.95）.The penetration rain rate and precipitation were consistent with a quadratic term function;the interception rate and trunk flow were.related to precipitation in a power function or logarithmic relationship.（5）The water-holding capacity of the litter under different stands was analyzed,and the maximum water-holding rate of the litter in the undecomposed layer showed:acacia（219.12%）>silk cottonwood（206.70%）>date palm（201.70%）.The effective storage capacity showed that Robinia pseudoacacia(6.26t·hm^-2)>Elaeagnus angustifolia(5.36t·hm^-2)>Euonymus maackii(3.79t·hm^-2).The maximum water-holding rate of the semi-decomposed layer of litter showed that Elaeagnus angustifolia（183.28%）>Robinia pseudoacacia（173.57%）>Euonymus maackii（171.81%）;the effective storage capacity showed that Euonymus maackii(5.33t·hm^-2)>Elaeagnus angustifolia(5.13t·hm^-2)>Robinia pseudoacacia(4.18t·hm^-2).The water uptake rate of dead litter in the undecomposed layer was in the order of Euonymus maackii(3.83t·hm^-2-h^-1)>Robinia pseudoacacia(2.85t·hm^-2.h^-1)>Elaeagnus angustifolia(1.95t·hm^-2·h^-1).The water uptake rate of dead litter in the semi-decomposed layer showed that Robinia pseudoacacia(2.82t·hm^-2·h^-1)>Elaeagnus angustifolia(2.79t·hm^-2·h^-1)>Euonymus maackii(2.78t·hm^-2·h^-1).The power function equation could provide a better simulation of the variation pattern of water uptake rate of the understory litter in different forest stands（R²>0.81）.（6）Based on the water balance,soil evaporation was the main subcomponent of water export from the woodland ecosystem throughout the study period,followed by stand transpiration.The water deficit status of Robinia pseudoacacia stand was the most severe during the observation period,followed by Elaeagnus angustifolia and Euonymus maackii.