| This research through long-term observation to the soil moisture of different phytocoenosium in Yanchi County of Ningxia province, determining the transpiration rate of main plants in growing season, study the precipitation in resent years as well as the soil evaporates, the thesis initially discussed the different vegetation type soil moisture distribution pattern and the change rule. and the major results is followed:(1)Through analyzing the precipitation in resent 45 years in Yanchi County, it shows average annual rainfall in growing season is 218mm, which is 80% of average annual rainfall. An annual effective rain day were primarily focused between May and October, were 21.7% of the annual rain days, and were 87.8% of the annual effective rain days. The average days of >5mm were 16.1 days, moderate rain and downfall was few, the average days of >25mm were only 1.4 days. Precipitation variability between 1961-2005 was 24.68%, Precipitation has a strong impact on vegetation stability. (2)Study the soil evaporation, water evaporation, and soil moisture, the relation as bellow: y = 53.405x2 - 16.796x + 4.094, R2 =0.9518. MLS Simulates the different rainfall amount to evaporate the experiment toindicate that, the accumulation water surface evaporates with theaccumulation soil surfaced road evaporates the existence conic sectionrelations.(3)Plants transpiration types as follows: A.dasystachys, Salix Mongolica Stuzevis single peak, S. alopecuroides L. is double peak, C.microphylla Lam., Artemisia ordosica Krasch and G.uralensis Fischis mixed. Transpiration rate: S. alopecuroides L.: 979.34mg·h-1·g-1, A.dasystachys: 685.88 mg·h-1·g-1. C. Komarovii Al. Iljinski: 574.16mg·h-1·g-1, Guralensis Fisch: 761.18 mg·h-1·g-1, Salix Mongolica Stuzev: 551.36mg·h-1·g-1, C.microphylla Lam.: 316.58 mg·h-1·g-1, Artemisia ordosica Krasch: 379.18mg·h-1·g-1. A.dasystachys, S. alopecuroides L. , Guralensis Fisch and C. Komarovii Al. Iljinski 4 kind of herbs class plant growth season transpiration weighs out donot be: 193.4mm/m2, 187.5mm/m2, 164.2mm/m2, 155.8mm/m2, The bush class plant growth season transpiration water consumption is: C.microphylla Lam.202.4mm/m2 , Artemisia ordosica Krasch215.6mm/m2, Salix Mongolica Stuzev226.9mm/m2.(4)Vertical distribution of soil moisture in Different research samples performance obvious layering. Seasonal variation is divided into three stages: May soil moisture weak dehydrate stage June-August on soil water consumption stage, September soil moisture slow recovery phase. Vegetation, atmospheric precipitation and terrain is the main factors affected changes in soil moisture.Through soil water balance, the evapotranspiration in different samples as follows: C.microphylla Lam. 193.63mm, Salix Mongolica Stuzev≤203.96mm, denuded land 179.61mm, Artemisia ordosicaKrasch 199.25mm, Guralensis Fisch≤193.54mm. A.dasystachys 187.42mm, C. Komarovii Al. Iljinski 249.49mm, S. alopecuroides L. 231.29mm, Fixed sand 167.22mm .Various water deficit occurred in different samples 2006. Accordingly, in Yanchi county sandy land, in addition to the normal C. Komarovii Al. Iljinski and S. alopecuroides L., the rest of the major plant communities evapotranspiration in growing season is less than the annual average rainfall, the state will show a surplus. Therefore, in terms of plant communities stability and soil water balance, water is an important ecological factor, It regulates the distribution of vegetation, structure and stability.(5) Soil moisture content seasonal variationcharacteristic can effectively slow down arid to plant's forcing of sandy land in yanchi,relaxes the soil drought and the atmospheric drought super imposition effect, has the promoter action to this area plant growth. But thedifferent vegetation is affecting the precipitation Evaporates sends thecondition in the soil different depth assignment and the surface, theprecipitation is affecting on the vegetation in the root level soilassignment the direction and the stable type.Plant growth and development depend on many environmental factors and climate conditions, and an area of dry and wet weather conditions mainly depends on precipitation and evaporation, sand vegetation succession process is the soil moisture and vegetation interactions evolving process. The different development degrees of desertification decide a corresponding soil vegetation distribution patterns.
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