| In order to find out the performance of Melastoma dodecandrum(Melastoma dodecandrum Lour) as a slop-protection plant,from 2005 to 2007,through field examination and plant introduction,the reproduction characteristics of Melastoma dodecandrum were observed,and the cultivation techniques were studies.Through the artificial precipitation test and the surface runoff test on the soil covered by Melastoma dodecandrum and the one covered by simulate vegetation canopy,the efficiency of decreasing soil erosion of Melastoma dodecandrum was tested and the characteristics of Melastoma dodecandrum which help to decrease soil erosion were analyzed;with the comparison with naked soil and honeysuckle rooted soil,through large-scale in situ direct shear test and the analysis of root volume and root strength,the shear resistance of the soil rooted by Melastoma dodecandrum was tested,the effect of Melastoma dodecandrum root system on the enhancement of the two parameters of soil shear resistance was analyzed.The effects of honeysuckle root system and Melastoma dodecandrum root system on soil conservation were compared;the correlation of root volume,root strength and the shear resistance was analyzed.The rationality of using conventional direct shear method and that of using large-scale in situ direct shear method for shear resistance were compared. The main findings are as follows:(The results below are all under certain conditions in this study.Those conditions would not be listed in order to save space.)1.The green period of mature Melastoma dodecandrum plant was slightly less than 10 months;the flowering period of mature Melastoma dodecandrum plant was slightly over five months.2.The seed dormancy existed;after some process,the germination rate would be up to 80%.The seed yield of Melastoma dodecandrum was 40.18g/m2;the theoretic seeding rate was 12kg/hm2;the coefficient of keeping a full stand of seedlings was 4.59;the propagation coefficient was 5599;the life span of Melastoma dodecandrum seed was less than 11 months.3.During the canopy expansion period of Melastoma dodecandrum,the best application rate of N, P2O5,K2O were respectively 0.638g/plant/month,0.448g/line/month,0.346g/line/month. 4.Melastoma dodecandrum was a light-loving plant,however,it could keep a good growth rate when the shading rate reached 42 percent.5.Melastoma dodecandrum could resist drought for two months in summer and autumn.6.The rate of decreasing soil erosion of soil covered by Melastoma dodecandrum was up to 97.90%; the rate of decreasing soil erosion of Melastoma dodecandrum canopy was 96.02%;the rate of decreasing soil erosion of the leaves was 90.64%.The effect of Melastoma dodecandrum leaves reducing soil erosion was 96.84%of the best potential effect of the leaves.The rate of reducing soil erosion caused by surface runoff of Melastoma dodecandrum root system was 87.55%,which was 15%higher than that of the honeysuckle root system which was 72.33%.The relation between erosion modulus and root length of Melastoma dodecandrum rooted soil,honeysuckle rooted soil and naked soil could be fitted into the conic curve:y=3.785x2-12.281x+10.501.The maximum capacity of enhancing erosion resistance of Melastoma dodecandrum was reached in terms of the root length per unit soil volume.7.The soil cohesion increments(Δc/kPa)of Melastoma dodecandrum rooted soil at the depth of 10cm,20cm,30cm,45cm were 32.41,17.17,11.89,3.04 respectively;the internal friction angle increments(Δφ/°) were 2.39,0.76,0.72,0.15;Δcs of Melastoma dodecandrum rooted soil at these depth were 1.87 times 2.11 times 2.64 times 1.74 times of those of the honeysuckle rooted soil,Δφs were 3.46 times,3.17 times,4.24 times 1.5 times of those of honeysuckle rooted soil.8.Compared with honeysuckle rooted soil,the root cross areas were slightly larger on the cross surfaces of four soil layers of Melastoma dodecandrum rooted soil;the average root strength and the effective rate of root tensile strength were much higher.These differences on the three aspects between the two types of soils resulted in the differences in soil shear resistance of the two types of soils.9.The relations between soil shear resistance(Δτ/kPa) of the four tested soil layers of Melastoma dodecandrum rooted soil and the root tensile strength(T/kPa) per unit soil area were as follows: 10cm layer,Δτ=0.9264T-31.111(A) 20cm layer,Δτ=0.3845T-0.3809(B) 30cm layer,Δτ=0.3699T+0.1187(C) 45cm layer,Δτ=0.3594T-0.1319(D) The constant in equation A was so large that it was a substantial difference from the mechanical model of soil shear resistance increment influenced by root system,Δτ=TN·(sinθ+cosθ·tanφ)·Ar/As=TN·δ·Ar/As,which was proposed by Wu,TH(1976) and then had been widely used in studies.10.The shear resistance values of undisturbed original soil measured by conventional direct shear method were smaller than those measured by large-scale in situ direct shear method.The diffferece would be higher when the soil density was low.There was regular abnormal occurrence about the values of soil shear resistance of Melastoma dodecandrum rooted soil at the depth of 10 cm by the conventional direct shear method.These results indicate that Melastoma dodecandrum has a good reproductive capability,high-density canopy cover,strong root system,certain degrees of drought and shade tolerance,excellent ability to reduce soil erosion,and enhance the soil shear resistance.All these above show a good comprehensive value for slope protection.
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