Study On Changes Of Soil And Community Characteristics In Highway Slopes At Early Stage Of Artificial Vegetation Restoration In Southern Shaanxi Province

Highway as a national fundamental infrastructure generates large numbers of excavationand filling slopes which results in soil and water aggravation. Vegetation restoration is a keycontent of ecological protection in the slopes and thus activates much concern. Based on theinvestigation approach of substituting ‘space’ for ‘time’, This paper investigated and analyzedthe soil, vegetation and seed bank of28sample spots in the highway slope of the southernShaanxi so as to clarify the vegetation characteristics, revolution direction and soilimprovement effect in different periods of the early stage of artificial vegetation restoration(0a,2a,5a,7a) and under different slope protection conditions as well. The main results are asfollows.（1）The soil in the28sampling spots locates in the highway slopes of the mountainousarea of the southern Shannxi, and is greatly lack of nutrients. The soil organic matter, total Ncontent are at deficiency or significant-deficiency level, and the available P at medium ordeficiency level; only available K content is at appropriate level. As the vegetation revolutiondevelops and the vegetation restoration proceeds, the soil organic matter and total N contentincreases with an insignificant level, and also shows a cumulating trend toward surface layer.Comparative analysis among three kinds of fertilizer and water retaining approach shows thatframework slope protection models are the most optimal one, net-suspended spray seedingprotection models the second, and arch+vegetation bags protection models the final one.（2）Soil aggregates at different restoration annual-stages (0a,2a,5a,7a) are prone tomacro aggregates (>0.25mm); as time proceeds ahead, both MWD and GMD of soilaggregates increases except the fractal dimension with opposite change trend. The soilimprovement based on artificial vegetation in the highway slopes of southern Shannxi showseffects after5years recovery with an insignificant level. The particle size mainly distributes atthe diameters <0.002mm, and the particle size fractions at0～10cm and10～20cm aredifferent. The correlation between the particle size distribution and fractal dimension issignificant or greatly significant, while both correlations with soil nutrient condition areinsignificant respectively. （3）The vegetation communities in the28sampled plots include52species of plantsbelong to22families and49genera. The families of Gramineae, Leguminosae andCompositae are in the majority. Among these families, Compositae plants is the most popularone (14species), Gramineous the second,(8species) and Leguminosae the third with sevenspecies. The communities mainly consist of annual or perennial herbaceous plants with rareshrubs. In the initial stage of artificial vegetation construction, the main vegetation types inthe community to be constructed should be the integration of shrubs and grass. The vegetationconstruction employment in the slopes should adopt the system integrating with the herb(Coronilla varia, Medicago sativa, etc.) and the bushes (Amorpha fruticosa and Ligustrumlucidum, etc.), as the system can increase the usage rate of water, light and nutrients, andimprove the stability of the community.（4）Vegetation specie density increases as the recovery time proceeds, and thevegetation coverage in sunny slopes is consistently more than that in shady slope. All thecommunity species number, species diversity index and soil organic matter content have verysignificant positive correlation with total nitrogen content respectively, while haveinsignificantly correlation with the available nutrient. The fractal dimension of aggregates hassignificant effects on species types. The diversity index has insignificantly negativecorrelation with fractal dimension of soil aggregates, moisture content and porosity. The soilnutrient and physical properties directly impact the changes of vegetation species, and furtherimpact vegetable species components and diversity.（5）The soil seed bank in the slopes composes of63vegetable species belonging to24families. Gramineae, Leguminosae and Compositae constitute the majority. Compositaeplants is the most popular one (18species), and more than90%are natural invasive species.The number of ground vegetation species and seed bank communities have a certaincorrelation relationship (R2=0.35, p>0.05). As time proceeds, their similarity coefficient(the number in same species) increases, and their richness index and diversity index showspositive correlation. The species, density, rich index and the diversity index of soil seed bankhave greatly significant correlation (p <0.01) with soil organic matter and total nitrogencontent; the types and density of the species are positively correlated with other availablenutrients and negatively correlated with fractal dimension (p>0.05). The characteristics of theground vegetation community and soil seed bank can reflect the soil characteristics on acertain extent; in turn the properties of the soil directly influence their communitycharacteristic.