| Karst areas in southwest China are large in area,widely distributed,complicated in topographic conditions,with high bare rock rate and shallow soil layer.The special karst geological environment and long-term unreasonable human activities have caused serious damage to the fragile ecosystem,and many places have formed the natural landscape of rocky desertification.The vegetation restoration measures with ecological economic species as the main species can balance the contradiction between ecology and economy in karst area.In view of this,the study selected Longtan Trough Valley in Youyang,Chongqing as the research area,and planted three hedges of Vicia villosa,Dolichos lablab L.,and Ophiopogon bodinieri in up,middle and down slopes respectively.The morphological and mechanical properties of different hedgerows roots in karst areas,the physical and chemical properties of root soil and aggregate characteristics were analyzed,and the strength of root-soil complex shear performance and soil separation ability were compared.The enhancement effect and influencing factors of different hedgerows roots on soil erosion resistance in karst trough-valley area were quantitatively evaluated.To quantify the role of root physical entanglement and biochemical effects in soil erosion control.The main conclusions are as follows:(1)The root index of Ophiopogon bodinieri was the highest,followed by Dolichos lablab L.,and the lowest for Vicia villosa.The roots of the three hedgerows were more developed in the middle and down slope than in the up slope.All the root morphological indexes were prominent in diameter class 0.5< d ≤1.0 mm.For Dolichos lablab L.and Vicia villosa,the dominant diameters of root length and root surface area were 0< d ≤0.5 mm.For Vicia villosa,the content of cellulose and lignin was higher than that of the other 2 kinds of hedgeroses,and the hemicellulose content was much lower than that of Dolichos lablab L.and Ophiopogon bodinieri.There were significant differences in root ultimate tensile strength among the three hedgerows in up,middle and down slopes,and the features were as follows: Ophiopogon bodinieri > Dolichos lablab L.> Vicia villosa.(2)Hedgerow roots can improve total porosity and organic matter.The enhancement of organic matter content by Dolichos lablab L.and Ophiopogon bodinieri was significantly better than that by Vicia villosa,and the enhancement of water stability of >0.25 mm aggregate by Dolichos lablab L.was greater than that by Ophiopogon bodinieri and Vicia villosa.The structural stability of the soil in the middle slope was better than that in the down slope.Soil bulk density,total porosity,non-capillary porosity and saturated water content in root zone were significantly correlated with root length and root volume in root morphological indexes,and root morphological indexes had a deeper effect on soil physical properties than root fiber content indexes.(3)The shear strength of Ophiopogon bodinieri complex was the best.Compared with CK,the cohesion of Dolichos lablab L.complex increased by 113.06%-124.37%,that of Vicia villosa complex increased by 51.56%-87.12%,and that of Ophiopogon bodinieri complex increased by143.39%-148.48%.The cohesion of the three hedgerow complexes and CK showed as follows:Down slope > middle slope > up slope.Soil bulk density and total porosity were significantly or extremely significantly correlated with the internal friction angle,in which the bulk density was positively correlated with the internal friction angle,while the total porosity was negatively correlated with the internal friction angle.The cohesion of Vicia villosa and Ophiopogon bodinieri complex and root length density,the cohesion of Dolichos lablab L.complex and root volume density showed significant positive correlation,with the highest correlation coefficient of 0.782.Principal component analysis showed that soil bulk density,total porosity,root surface area density,lignin content and tensile strength could better reflect the strength of shear strength of composite.The comprehensive score of the shear strength of Ophiopogon bodinieri complex was the highest.(4)The soil separation capacity of root-soil complex was significantly lower than CK.The total effect of hedgerow roots on soil separation ability was more than 40%,and the contribution of root physical consolidation to soil separation ability was 70.46%.The contribution of root biochemical effect to soil separation ability was 29.54%.The soil separation rates of Dolichos lablab L.complex were middle slope > up slope > down slope,and the soil separation rates of up slope and middle slope were 1.66 times and 1.73 times of that of down slope,respectively.The soil separation rate along the Ophiopogon bodinieri complex decreased with the slope position decreasing,which was in the order of up slope > middle slope > downr slope.The soil separation rate along the Ophiopogon bodinieri complex on the up slope and middle slope was 2.82 times and 2.16 times of that on the down slope,respectively.Principal component analysis showed that root surface area density,lignin and root volume density,root length density,tensile strength could explain the soil separation resistance of root-soil complex.In addition,the comprehensive score of soil separation resistance of the two hedgerow complexes was the highest in down slope.In conclusion,the dense distribution of roots and the large number of roots required by Ophiopogon bodinieri,combined with its good tensile properties,resulted in the enhanced effect of its roots on soil shear performance and the resistance control effect on soil separation process,which were higher than other hedgerows.Root length density,root surface area density and tensile strength have the greatest influence on soil shear performance and soil separation ability,which can be used as the key factors to evaluate the erosion resistance of surface soil in karst troughs and valleys.In addition,the good soil environment on the downslope made the roots of the three hedgerows more developed,and their root length density was significantly higher than that on the upper and middle slopes.When implementing plant measures in karst troughs and valleys,planting on the low and gentle slopes is more effective in soil and water conservation. |
