Studying On The Process Of Nitraria Tangutorum Nebkahas' Growth Between Oasis And Desert

In order to study its morphological changes, vegetation status and soil physicochemical characteristics in Nitraria earth bags development process, comprehensively understanding the law of Nitraria growth, finding suitable soil physicochemical environment which benefit its growth, and providing data foundation and theoretical basis for natural vegetation conservation and restoration, utilization of Nitraria against desertification in Minqin region as well as other arid and semi-arid areas. This paper adopted the method that substituting time with space, selected Nitraria earth bags with different development phases in desert-oasis transitional zone in Minqin, research on the following item: (1) Nitraria earth bags/s morphological characteristics in different development stages; (2) soil morphological characteristics in different development stages; (3) Plant growth characteristics in different development stages; (4) Plant community structure characteristics in different development stages. The result as following:(1)Nitraria tangutorum'development process is a morphological changing process of the earth bags. In this process, bags height, size, volume were all gradually increased, and the bag slope and length are increased, windward slope length is alwa- ys shorter than the leeward slope, the long axis and short axis coordinated growth on the horizontal scale, the long axis is steady growth, while the short axis has increased from rapid to the slow. Bags height and horizontal scale are marked by the strong relationship into a weak correlation, correlation between parameters changes from strong to weak.(2)Nitraria earth bags development process is a changing process of soil morphological characteristics. In this process, soil moisture increased, Soil particles mainly consist of fine sand and very fine particles of sand (0.1-0.05) in 0-70cm soil layers each stage, grain whose size is 0.5-0.25mm and fine sand content decreased, very fine sand, silt and clay content were increased, gravel content in the developmental phase greater than in the initial and maturity, coarse sand content was not significant in each stage. Soil total salinity was increased, pH value in the initial and developmental phase were greater than in the maturity. Soil organic matter and total nitrogen in the developmental phase were greater than in the initial and maturity, available phosphorus increased while available potassium decreased. Soil moisture, total salinity, organic matter and available potassium play a major role in the soil physical and chemical properties.(3)Nitraria earth bags development process is a changing process of plant characteristics. In this process, Nitraria tangutorum average density decreases, while the average height, shoot length, biomass and coverage in the developmental phase were greater than in the initial and maturity. Nitraria tangutorum root biomass whose diameter is more than 3 mm mainly occurred in the 0-50cm soil layer, accounting for more than 92%;The most of root biomass whose diameter between 1 mm and 3 mm distributed in the 0-40cm soil layer, which accounts for 83.32% in the initial phase, 86.75% in the developmental phase and 85.32% in the mature phase of all root biomass whose diameter between 1 mm and 3 mm; root biomass whose diameter less than 1 mm mainly distributed in the 0-20cm soil layer at the initial and mature period of bags, accounting for 49.73% and 52.89% respectively, while in the developmental phase, its root biomass distributed in 20-40cm soil layer, accounting for 47.66%. Soil salinity, soil organic matter, total nitrogen, content of gravel and coarse sand are no significantly related with Root biomass. Root biomass increased with the increasing of soil moisture, available phosphorus, fine sand, silt and clay content, pH value, available potassium, and the sand and fine sand content. Root biomass whose diameter more than 3 mm is not significantly related with the soil physical and chemical activities.(4)Nitraria earth bags development process is a changing process of community characteristics. In this process, diversity index, evenness and ecological dominance index are low each stage, desert vegetation species compose simple, structure level is significant, with two layer film: shrub layer and herb layer. Prominent dominant species extrude with instability. Changes in species populations and interspecific encounter rates are considerable in different development stages. Level of species diversity in the medium and maturity was significantly higher than in the initial, species are more abundant, this is mainly the water and soil nutrient status in the medium and maturity better than in the initial. Species evenness in the initial and maturity was significantly higher than in the medium.