Study On Difference Of Soil Reinforcement Mechanical Characteristics Among Four Shrubs And Semi-shrubs Coupling Roots And Overground Branches And Leaves

The study of soil reinforcement mechanical characteristics are of important theoretical and practical significance for ecological construction in composite regions bearing wind and water erosion of Inner Mongolia. Four widely cultivated shrubs were chosen in our study,such as Caragana microphylla Lam.,Salix psammophila C.Wang et Ch.Y.Yang, Artemisia sphaerocephala Krasch. and Hippophae rhamnoides Linn.. To research the difference of root tensile characteristics, root-soil interface friction characteristics, root-soil composite shear characteristics and overground part windproof characteristics among the four shrubs, we used methods of whole plant mining, direct shear test, axial tensile test and natural wind speed measuring in this study. The research purpose was to reveal the mechanism of soil reinforcement of the four shrubs and their interspecific difference, and thereafter to provide the theoretical basis for the ecological restoration in research regions. The main achievements of our study are as following:1. Root tensile characteristics of Caragana microphylla Lam. and other three shrubsThe mechanism in plant root for resistance to the external tension contains two different components, which are tensile force of single direct root and lateral root branch respectively. They play important roles in soil reinforcement with interrelation and significant difference at the same time. Our research revealed that the tensile force and tensile strength of the four shrubs’ single direct root was stronger than those of lateral root branch, and their gap varied among different plant species, characterized by Caragana microphylla Lam. > Salix psammophila C.Wang et Ch.Y.Yang > Artemisia sphaerocephala Krasch. > Hippophae rhamnoides Linn.. Growing season conducted significant effect on tensile force of both single direct root and lateral root branch. The tensile force of single direct root was higher during the period of vigorous growing season than early growing season in Caragana microphylla Lam. and Hippophae rhamnoides Linn., however, Salix psammophila C.Wang et Ch.Y.Yang and Artemisia sphaerocephala Krasch. were opposite. When compared in lateral root branch, the tensile strength was higher during early growing season than vigorous growing season in Caragana microphylla Lam., Artemisia sphaerocephala Krasch. and Hippophae rhamnoides Linn., and Salix psammophila C.Wang et Ch.Y.Yang was in contrast. Inaddition to, with increasing of root diameter and soil moisture content, the tensile strength decreased in both single direct root and lateral root branch, therefore, they were both enhanced when load rate increased.2. Root-soil interface friction characteristics of Caragana microphylla Lam. and other three shrubsRoots and soil interface friction characteristics including two parts, respectively is the shear friction characteristics and drawing friction properties. Significant effect was found between root-soil interface shear characteristics and vertical load, soil moisture content and soil dry density with significant variation among plant species. Under the same experimental conditions, the order of the root-soil interface friction coefficient among the four shrubs was as Artemisia sphaerocephala Krasch. > Caragana microphylla Lam. > Salix psammophila C.Wang et Ch.Y.Yang > Hippophae rhamnoides Linn., and their cohensive force’ order was as Caragana microphylla Lam. > Artemisia sphaerocephala Krasch. > Salix psammophila C.Wang et Ch.Y.Yang > Hippophae rhamnoides Linn.. The root diameter, soil dry density and soil moisture content had significant effect on root-soil interface tensile strength, when no significant effect was found between conditions with different withdrawing speeds. The four shrubs’ root-soil interface tensile strength decreased with increasing of root diameters, and increased with increasing soil dry density, and increased first and then decreased with increasing soil moisture content.3. Root-soil composite shear characteristics of Caragana microphylla Lam. and other three shrubsThe shear strength and cohensive force of the four shrubs were higher than those of pure soil. Compared under the same vertical load(12.5 kPa), the order of the four shrubs was as Caragana microphylla Lam. > Salix psammophila C.Wang et Ch.Y.Yang >Artemisia sphaerocephala Krasch. > Hippophae rhamnoides Linn. > pure soil.The vertical load, root diameter, soil moisture content, soil dry density, growing season and root layout had significant effect on Caragana microphylla Lam., Salix psammophila C.Wang et Ch.Y.Yang, Artemisia sphaerocephala Krasch. and Hippophae rhamnoides Linn., with significant variation among plant species. The four shrubs’ root-soil composite shear strength increased with increasing vertical load, and decreased with increasing soil moisture content. The four shrubs’ root-soil composite internal friction angle decreased with increasing soil dry density while their cohensive increased with increasing diameter and soil dry density. The effect of root layout on root-soil composite shear strength was as 45° reverse direction > vertical direction > 45° sidedirection > 45° forward direction.4. Difference of soil reinforcement mechanics characteristics among Caragana microphylla Lam. and other three shrubs coupling roots and overground branches and leaves and their dominant factorsUnder the conditions of modeling drought situation in spring and rainstorm situation in summer, the comparative order of the soil reinforcement benefit coupling roots and overground branches and leaves among the four shrubs and soil reinforcement ideal model was as soil reinforcement ideal model > Salix psammophila C.Wang et Ch.Y.Yang> Caragana microphylla Lam., Artemisia sphaerocephala Krasch. > Hippophae rhamnoides Linn..The tensile mechanical characteristics, cumulative root length and plant windproof characteristics were the main dominant factors of soil reinforcement coupling roots and overground branches and leaves in Caragana microphylla Lam. and other three shrubs,and the tensile mechanical characteristics and cumulative root length played more significant roles than plant windproof characteristics. The second important dominant factors were root-soil composite shear characteristics and root-soil interface friction characteristics, and the shear characteristics were more important than interface friction characteristics.