Study Of Response To Drought Tolerance And Hydraulic Lift Of Zygophyllum Xanthoxylum

Relationship between plant and water in arid environment is a hotspot in physiology and ecology research, but the mechanism about hydraulic redistribution is still undiscovered.The biology and physiology characteristics were investigated by PEG treatment and water control of Zygophyllum xanthoxylum. Hytraulic lift of Z.xanthoxylum was identified by using the split-root apparatus that upper pot was fixed on the lower pot. The results are as follows:(1)The holding moisture capacity of Z.xanthoxylum during the seedling stage decreased under drought stress. There is a significant correlation between MDA and PEG concentrations(P<0.05). The concentration of proline inceased rapidly but dissoluble sugar decreased under drought stress . The severe drought stress(30% of PEG) promoted the accumulation of Na⁺ in the leaves but not to K⁺ and Ca²⁺. It could been concluded that the proline was the primary osmotic adjusting materials and Na⁺ reacted under the severe drought stress.(2)The growth of two years old Z.xanthoxylum was restrained when the soil water content was below 13%. The distributive proportion of biomass changed with the decease of soil water content, leading to the increase of ratio of root to crown and biomass of thin roots. The proportion of leaves decreased by contrasting to the stems under severe drought stress(3% of soil water content).(3)The leaf water potential of two years old Z.xanthoxylum reached -4.20 MPa and -3.10 MPa under severe drought stress after 20 days and 45 days. The leaf relative water content and the holding moisture capacity also decreased under severe drought stress. The daily water consumption decreased with the soil water content. The variation of water consumption in a whole day is a level line which showed the low water consumption at different periods.(4)The proline and the dissoluble sugar in the leaves of Z.xanthoxylum during the stage of two years increased significantly under severe drought stress. The accumulation of proline did not occur in the stems and roots while the dissoluble sugar decreased under severe drought stress. Na⁺ also increased in the leaves under the severe water stress but needed a continuous times and Ca²⁺ decreased under the same condition. K⁺ increased under severe water stress and could happen under 8% of soil water content, but it needed a longer time(about 60 days). Na⁺ increased in the stems but did not to K⁺ and Ca²⁺ decreased. The accumulations of Na⁺. K⁺ and Ca²⁺ did not occur in the roots. The severe drought stress promoted the accumulation of MDA and the increase of membrane permeability in the leaves of Z.xanthoxylum during the stage of two years.(5)The hytraulic lift of Z.xanthoxylum was identified effectively by the split-root apparatus. The difference between the upper soil water potential and the lower soil water potential was at 2.41 MPa When the hytraulic lift occurred. The soil volume content and soil water potential in upper pot increased in the daytime and decreased at night according to continous observation of 17 days. It is concluded that the hytraulic lift of Z.xanthoxylum occurred in the daytime. The quantity of hytraulic lift varied due to different methods of treatment. The order was arranged: restraining soil transpiration of upper pot> soil transpiration of upper pot> restraining plant transpiration and restraining soil transpiration of upper pot.(6)The occurrence and quantity of hytraulic lift could be promoted by transpiration. If the quantity of water absorbed by roots in the wet soil was more excessive than water consumed by transpiration. At the same time, the root water potential in dry soil was higher than soil water potential. Water could flow into the roots in the dry soil by reverse water potential grads from leaves or by direct movement from roots in the wet soil, and then released in the soil. The osmotic adjusting materials could adjust hytraulic lift of Z.xanthoxylum by the effects of the leaf water potential and soil water potential in the upper pot. Finally, we try to summarize the conception of Hydraulic redistribution.