Study On Root Architecture And Mechanical Properties Of Root-soil Complexes Of Common Shrub Species In Karst Area

Root system can improve soil strength and inhibit the occurrence of shallow landslides.The effect of root system on soil consolidation and slope protection mainly depends on the root system configuration,root anti-tension and the interaction between root system and soil.In this study,field investigation and laboratory experiments were used to study the common shrubs in central Guizhou.The factors affecting the soil consolidation ability of plant roots were analyzed from four aspects: root architecture,single root tensile mechanical properties,whole plant tensile properties and rootsoil interface friction characteristics.The main results are as follows:(1)The root topographic index of the three shrubs tended to be 1,and tended to fish-tail branching mode.The adaptation strategies of Pyracantha fortuneana,Indigofera amblyantha and Cassia bicapsularis to karst habitats were similar.They all adapted to shallow karst soil and bare rock habitats by reducing root branching and increasing root connecting length.In addition,the root systems of the three shrubs were unevenly distributed horizontally and uncertain.(2)The average ultimate tensile strength and tensile strength of Rhamnus heterophylla were significantly lower than those of Mulan blue and Pyracantha fortuneana.The average tensile strength of Indigofera amblyantha and Pyracantha fortuneana was 1.63 and 1.76 times higher than that of Rhamnus heterophylla,respectively.The average ultimate elongation of Pyracantha fortuneana was 1.22 and 1.35 times higher than that of Indigofera amblyantha and Rhamnus heterophylla,respectively.The ultimate tensile strength of single root of three shrubs was positively correlated with root diameter by power function.Tensile strength and ultimate elongation had no significant correlation with root diameter.The ultimate tensile strength of single root of Pyracantha fortuneana with different spacing was 10 cm > 5 cm > 15 cm,and that of single root of Indigofera amblyantha with different spacing was 10 cm > 15 cm > 5 cm.The ultimate tensile strength of Pyracantha fortuneana and Indigofera amblyantha was the largest when the spacing was 10 cm;the ultimate tensile strength of single root of Rhamnus heterophylla was negatively correlated with the spacing,and the ultimate tensile strength of single root with three spacing was 5 cm > 10 cm > 15 cm.With the increase of the standard distance,the tensile strength of single root shows a decreasing trend.The ultimate tensile strength of single Rhamnus heterophylla had no significant difference between the two tensile rates,and the tensile rate had no significant effect on the ultimate tensile strength of single Rhamnus heterophylla.Most stress-strain curves are convex curves with decreasing slope.At the beginning of tension,stress and strain increase linearly.With the increase of strain,stress and strain gradually deviate from linearity and change to non-linearity,and the slope of stress-strain curve decreases gradually during drawing.The root system ruptures until the ultimate stress is reached.The stress-strain curve of the root system of Indigofera amblyantha has a multi-peak phenomenon.(3)There are two forms of friction failure and pull-out failure in the test results of friction characteristics of root-soil interface.The process curve of friction failure(displacement-pull-out force curve)can be divided into three stages: sharp rise,sharp decline and slow decline.The process curve of pull-out failure is similar to that of single tensile process.The single pull-out force of Indigofera amblyantha,Pyracantha fortuneana and Rhamnus heterophylla increased with the increase of root diameter.In the range of 15%~25% water content,the maximum tensile resistance of Indigofera amblyantha root system The pullout force first increases and then decreases with the increase of soil water content.The pullout force of roots of Pyracantha fortuneana continues to increase with the increase of soil water content,and the pull-out resistance of the roots of Rhamnus heterophylla showed a decreasing trend with the increase of soil water content.and the pullout force of the roots of different leaf buckthorn increases with soil moisture content.Tthe optimum moisture content of different tree species varies.In the range of soil dry density of 1.18g/cm3~1.28g/cm3,the single-strength pull-out force of the three shrubs increased monotonously with the increase of soil dry density.(4)The main root of Pyracantha fortuneana root system is obvious.The pullout resistance of the whole plant increases linearly and sharply with the increase of the pull-out displacement at the initial stage of pull-out.With the continuation of pull-out,the pull-out resistance reaches its peak at 5-10 cm of the pull-out displacement.When the maximum pull-out force is reached,the pull-out force decreases in wave form.There is no obvious main root in the Lindera communis,and the whole drawing process is similar to that of Pyracantha fortuneana,but the fluctuation of the drawing force-displacement curve of the f Lindera communis tree is small.When the drawing displacement is 6-10 cm,the drawing resistance reaches its peak value.(5)The results of self-made model root pull-out test show that the more lateral roots,the longer the length of lateral roots,the greater the pull-out resistance,and the longer lateral roots increase the contact area between roots and media.When the angle between lateral roots and main roots is 30 degrees,the pull-out force is the largest,followed by 60 degrees,and the pull-out force is the smallest when the angle between lateral roots and main roots is 90 degrees.The results showed that the pull-out resistance of vertical roots was better than that of horizontal roots.(6)Under the condition of similar root structure characteristics such as root branching and root connecting length,the anti-tension and root-soil friction of Pyracantha rhamnoides root system are superior to that of Pyracantha multiflora,which indicates that Pyracantha rhamnoides root system is superior to Pyracantha multiflora in retaining soil and preventing shallow landslides.