Study On The Drought Tolerance Characteristics Of Three Shrubs Based On The SPAC System In Loess Plateau Region

In order to provide proof for tree species selection in the course of vegetation rehabilitation in arid and semi-arid regions, the paper experimentized a series of studies on Shepher.dia argentea, Hippophae rhamnoides, Atraphaxis mandshurica in Loess Plateau Region, which is of significance to realize regional sustainable development, based on the observation of water movement in the system of Soil-Plant-Atmosphere Continuum.The main topics of this paper as follows:dynamical rules of soil moisture and atmosphere moisture; water potential changes and principles of water movement in the SPAC system under water stress; transpiration characteristics of different plants under water stress; discriminant analysis of the mechanism of drought tolerance of plants.Main conclusions are summarized as follows:(1) Precipitation was uneven in growing season in the experimental forestlands. Soil drought and water for plants growth was restricted from the lack of precipitation during the vigorous growth period.(2) As soil drought got intensified, the daily changes of leaf water potential changed from single-peak curve to double-peak curves. Considering the daily change range of leaf water potential, the paper found that three shrubs have different abilities to adapt to arid environment:Hippophae rhamnoides> Shepherdia argentea> Atraphaxis mandshurica. Moreover, air temperature and relative humidity were main meteorological factors effecting leaf water potential of different plants under different water stress(3) With increasing of soil water stress, the daily changes of photosynthesis rate of Hippophae rhamnoides and Shepherdia argentea changed from single-peak curve to double-peak curves. However, that of Atraphaxis mandshurica changed back and forth between single-peak curve and double-peak curves. By comparison, photosynthesis rate of Hippophae rhamnoides was highest under the same water gradient, which showed that Hippophae rhamnoides was high transpiration plant, of which stoma adjustment ability was better than two others.(4) By measuring the water potential in different interfaces of the SPAC system, the resistance of water transferring was calculated. The results showed that the hydraulic resistance from leaf to atmosphere was greater than that from soil to leaf. In addition, the hydraulic resistance in leaf-atmosphere or soil-leaf interfaces was:Atraphaxis mandshurica>Shepherdia argentea> Hippophae rhamnoides.(5) The wilting coefficient was 3.82% of Shepherdia argentea,3.63% of Hippophae rhamnoides, 3.87% of Atraphaxis mandshurica. The soil water use efficiency of potted plants was all above 85% and that of Hippophae rhamnoides was highest 87.25%. The ability to resist drought of three shrubs was sized up according to soil water depleted index as following:Hippophae rhamnoides> Shepherdia argentea> Atraphaxis mandshurica. Besides, based on the discriminant models between leaf water potential and soil water content or soil water potential, three shrubs were all plants that had low water potential to delay dehydration.