Study On Relationship Between Vegetation Dynamic And Water Condition In Horqin Sandland

The different types of vegetation in Horqin sandland were taken as experimental materials and measured by using traditional investigative methods in the field ecology. Relationship between vegetation dynamic and water condition was studied based on the follow views: changes of environment conditions, components of vegetation, plant diversity, life-forms of vegetation, characteristics of the vertical and horizontal structure of vegetation, trends of plant growth and characteristics of plant physiological activities. Some results were showed as follow:1. Changes of Environment ConditionsThe experimental site was located in Naiman country, inner Mongolia Autonomous Region, in which it is the semi-arid climate and environmental characteristics. The rainfall was highest in August, and lowest in September. The temperature was highest in July, and lowest in May. The average soil moisture content in the semi-fixed dune land in June was less than that in August and equal to that in September. The average soil moisture content in the natural reconverted grazing land was lowest in September, and highest in August. The average soilmoisture content in the natural reconverted farmland was lowest in August, and highest in June.2. Components, Diversity and Life Style of VegetationThe components of vegetation in the experiment site were 26 species belonging to 9 families and 25 genera. Species diversity in three types of vegetation were relatively higher in August, and lower in May. Species diversity of vegetation was highest in the reconverted grazing land, lower in the semi-fixed dune land, and lowest in the natural reconverted farmland. The stability of vegetation in the reconverted grazing land was relatively high and strong buffering function to changing environment among three types of vegetation. The biological spectrum in different types of vegetation was obviously different, and changed with the season. In the biological spectrum of vegetation in Horqin sandland, the ratio of annual grass was always largest, perennial grass was the next, shrubs were lowest.3. The Structure of VegetationThe structure of vegetation usually consisted of a vertical structure and a horizontal structure of vegetation. The semi-fixed dune land consisted of shrub layer and herb layer. The dominant species of them were Artemisia halodendron Setaria viridis respectively; The reconverted grazing land and the natural reconverted farmland consisted of herb layer and microbiotic crust layer, but itsmain layer was herb layer. The dominant species of them were Cenchrus calyculatus Artemisia scoparia respectively. The horizontal structure of three different vegetation in the experiment site manifested out the mosaic characteristics. The coverage of annual grasses perennial grasses and shrubs in three types of vegetation ranked of the different level in different seasons. This was mainly due to the difference of dominant species of vegetation in different seasons.4. The Growth Dynamic of VegetationThe number of species height coverage and aboveground biomass of three types of vegetation increased constantly from May to August; The density of species declined from June to July, it was related to the decrease of rainfall in July and the competition of species for water and other nutrients. The growing period of shrubs was from May to July, and the shrub growth slowed down from July to August. The coverage of herbs in August was highest because the rainfall (62.8mm) was biggest in Horqin sandland. It was showed that dynamic growth of herbs in Horqin sand depended on rainfall in a certain extent.5. The Eco-physiological Characteristics of Dominant SpeciesArtemisia halodendron, Artemisia scoparia and Cenchrus calyculatus were the dominant species in three types of vegetation. The intercellular CO₂ concentration of the three species were lower than those of other species. However, the photosynthetic rate, transpiration rate, water use efficiency, Stomatalconductance and water potential of the three species were higher than those of other species. It was the mechanism that the three species became dominant species to adapt the dry environment.Based on the above, the structure the growth dynamic and the eco-physiological characteristics of vegetation was studied by the methods of ecology and plant physiology in this paper. These results were important to the practice of vegetation succession in natural restoration in Horqin sandland and the theory on the rehabilitation of degraded ecosystems.