Effect Of Salix Psammophyla Roots On Soil Anti-erosion And Its Mechanisms In The Water-wind Erosion Crisscross Region On The Loess Plateau

Vegetation construction is one of the most effective measures to prevent soil erosion in the wind-water erosion crisscross region of loess plateau.The belowground roots would play an important role in controlling soil erosion by vegetation.The present study selected Salix psammophyla,which is a native shrub in the wind-water erosion crisscross region of loess plateau,as the research object.Through field investigation,field location observation,laboratory experiments of simulated rainfall and wind-tunnel,distribution characteristics of Salix psammophyla roots,root effects on soil water and wind erosion were systematically studied.Internal mechanisms of the roots to resisting soil erosion were revealed.Relational equation between Salix psammophyla roots and water erosion,wind erosion,and interactive effects of water and wind erosion were built.The aim of the present study was to provide scientific basis for constructions of sand-living vegetation and ecological environment in the water-wind erosion crisscross region.The main conclusions are as follows:1.Distribution of Salix psammophyla roots in soil space presented a shape of inverted pyramid.The vertical distribution of roots mainly located in 0⁴0 cm soil layer and the horizontal distribution mainly concentrated in horizontal distance of 0⁸0 from the root base.Proportion of the roots which diameter was less than 1 cm could reach as 51.00%in total roots,and mainly distributed in soil depth of 0²0 cm and horizontal distance of 4¹20 cm from the root base.2.Salix psammophyla roots ameliorated properties of hydraulic characteristics,improved soil critical shear stress,increased ability of soil to resisting water erosion.The roots prolonged the initial time of runoff,increased soil infiltration rate,decreased overland flow velocity,Reynolds numbers,unit stream power,and increased overland flow depth,flow shear stress and drag coefficient.The roots increased soil critical shear stress and decreased soil erodibility.Compared with bared soils,the critical shear stress of root-permeated soils averagely increased by 4.19 times and parameters of soil erodibility averagely decreased by50.83%.Under the condition of laboratory simulating rainfall experiments,the values of sediment reduction effect of the roots were recorded as maximum of 66.52%,minimum of11.39%and the average of 35.62%.During the entire period of water erosion observations in filed,the values of sediment reduction effect of the roots were recorded as maximum of69.41%,minimum of 4.38%and the average of 19.75%.Water erosion observations in field confirmed the results of laboratory experiments of simulated rainfall.3.Salix psammophyla roots significantly increased ability of soil to resisting wind erosion through controlling sediment transport flux in near surface.The roots had little influence on characteristics of sediment transport flux profile and distribution of sediment transport flux with ground height.However,the roots reduced the flux of sediment transport in different ground heights.Compared with bared soils,the flux of sediment transport in different ground heights for root-permeated soils could averagely reduce by 21.58%and 39.38%at wind speed of 11 m s^-1 and 14 m s^-1,respectively.Under the condition of laboratory simulated wind-tunnel experiments,the average value of effectiveness of anti-wind erosion by the roots was recorded as 26.87%.During the period of wind erosion observations in field,the roots reduced intensity of wind erosion.Based on radionuclide of ⁷Be tracing technique,the average values of effectiveness of anti-wind erosion by the roots was recorded as 4.66%.4.Salix psammophyla roots weakened the effects of wind erosion on water erosion,and the linear equation could preferably reflect the relationship between soil erosion rate and root characteristic parameters.With the increasing interactive levels of wind and water erosion,e influence of the roots on soil infiltration,runoff and dynamic characteristics of overland flow seemed to be weakened.The roots changed the trend of soil erosion rate with rainfall duration.Different from the bares soils which soil erosion rate showed a fluctuated increase with the prolonged rainfall duration,the soil erosion rate of the root-permeated soils first increased,then decreased and finally tented to stabilize.Under the condition of laboratory experiments of simulating wind-tunnel and rainfall,the values of sediment reduction effect of the roots was recorded as maximum of 61.56%,minimum of 6.53%,and the average of 37.12%.Moreover,with the increasing interactive levels of wind and water erosion,the sediment reduction effect of the the roots increased.The linear equation could preferably express the relationship between soil erosion rate and root characteristic parameters?root weight density,root length density and root surface area density?.