Study On The Soil Reinforcement Of Four Plants Roots Damaged By Shear-tensile Combination

Four widely cultivated plants were chosen in our study,The taproots and lateral roots of Caragana microphylla,Salix psammophila,Hippophae rhamnoides,Artemisia ordosica were selected as subjects.The combined mechanical properties of shear-tensile were observed and analyzed,the evaluation index system was established,and the effective soil and water conservation index was calculated.This paper can improve the mechanical theory of soil reinforcement by roots system,which has important theoretical and practical significance for accurate vegetation construction in coal mining subsidence area.The main conclusions of our study are as following:(1)There were significant differences in the mechanical properties of the ultimate shear-tension combination of single roots of the four plants,and the root system of Caragana microphylla had the strongest combination of shear-tensile combination ability.And there is a positive power function correlation between the ultimate combined shear tensile force and root diameter,and a negative power function correlation between the ultimate combined shear-tensile strength and root diameter.The content of main chemical components in plant roots varied with root type and root diameter.The cellulose,The roots of Caragana microphylla had the largest cellulose,hemicellulose and brown cellulose,while Hippophae rhamnoides had the largest lignin content and wood-fiber ratio.(2)Plant single roots died after being damaged by combined shear-tensile forces,and sustained damage decreased more than after instantaneous damage.The number of surviving roots with lateral-roots decreased more than that of taproots,mild damaged was greater than severe damaged.Different self-repair time had no significant effect on the survival rate of single root damage after self-repair.In addition to Artemisia ordosica,the decline in activity of other three plants after single root damaged gradually decreased with the extension of self-repair time.The decrease of single root activity after severe damaged was greater than that after mild damaged.Under the same continuous shear-tension combined force damage,there was no significant difference in the degree of reduction of relative daily growth rate of taproots and lateral-roots.After 12 months of self-repair,the relative daily growth rate of Caragana microphylla,Hippophae rhamnoides and Artemisia ordosica were still less than 60%of parallel control.The relative daily growth rate of single root of four plants decreased with the increase of root diameter,and the fine root had stronger self-repairing ability.(3)After a single root withstand instantaneous or continuous damaged and self-repaired,the increase rate of ultimate combined shear-tensile force and strength of damaged single root were less than that of the parallel control.There was a positive power function correlation between the ultimate shear-tensile force and root diameter,and a negative power function correlation between the ultimate shear tensile strength and root diameter,which was the same as that before damage,and the mechanical properties of single root did not change after self repair.The damage had a greater inhibitory effect on ultimate shear-tension combined force of the lateral-root.The growth rate of the ultimate combined shear-tensile force and strength of single root after severe damaged was significantly lower than that of mild damaged.The single roots of four plants damaged and self-repaired,The ultimate combined shear-tension force and strength increased with the extension of self-repairing time,but the growth rate was slower for continuous damage.After instantaneous or continuous damaged and self-repaired,the ultimate combined shear-tensile force and strength of the four plant roots were still significantly lower than the parallel control,and complete self-repair was not achieved.(4)After partial roots of plant was damaged,the growth status of plant height,crown width,branch length and diameter were all inhibited,and their growth rates were all shown as parallel control>25%damage>75%damage.Partial roots damage had significant effects on photosynthetic and physiological characteristics.The more damaged the root system was,the lower the net photosynthetic rate,intercellular CO₂concentration,stomatal conductance and transpiration rate were.And with the passage of time,there was a trend of first rising and then falling.The activities of MDA,POD and SOD were higher in the first 10 days,which indicated that the excessive reactive oxygen species were removed after partial roots damaged.After 75 days of partial roots damaged,there was no significant difference between control and two partial damage degrees.(5)The evaluation indexes were selected,which were closely related to erosion control,including the axial tensile mechanical properties of single root,the shear-tensile resistance combination of single root,the main chemical components of roots,the shear resistant properties of the whole root system,the growth properties of root system under adverse conditions,and the wind-proof properties of above-ground branches and leaves of plants.And constructed an evaluation system through the analytic hierarchy process.According to the comprehensive evaluation results,Salix psammophila was the preferred plant species for wind erosion protection;Caragana microphylla was the preferred plant species for composite erosion protection;Salix psammophila had the largest effective persistent consolidation index,and was the preferred plant species for ecological restoration and vegetation reconstruction in semi-arid area.So,in the areas dominated by the three erosion types,Salix psammophila and Caragana microphylla as the dominant species,and the combination of Hippophae rhamnoides and Artemisia ordosica,was a long-term vegetation model for soil and water conservation.