Physiologic Responses of Haloxylon aphyllum to Consecutive Tensions of Dryness and Study of Their Role in Improving Resistance to Dryness of Vase Twigs

Osmotic and elastic parameters of Haloxylon aphyllum branchlets after inducing dryness were studied. The study of changes of water relations parameters with the aim of improving resistance to drought of this species through inducing chronic dryness and clarification of physiologic mechanisms of this plant in response to a low water and dryness are among the objectives of this study. For this purpose, the method of pressure chamber was employed. By this method, the pressure-volume curves were drawn and through their analysis, plant water relations parameters were obtained. A relatively mild dryness was induced to twigs through a lack of irrigation. It was such that after two weeks, the potential of the water of the branchlet of H. aphyllum twigs reached to -16.5 bars. A very intensive dryness was also induced to that but after four weeks of prevention from irrigation; it was such that the potential of the water of H. aphyllum branchlet was diminished to -27.2. A relatively mild dryness was repeated for six terms and a relatively harsh dryness for eleven consecutive periods. In both series of experiment, the potential of water of control twigs were being watered every two days once, remained fixed at about -12.7 bars. Based on the results, though the relatively mild dryness induction to twigs of this type of Haloxylon, made the increase of elastic property of branchlet textures but it had not a meaningful impact on its osmotic potential. Although the application of a relatively intensive dryness reduced the osmotic potential of H. aphyllum branchlets but at the same time, it increased the elasticity of the tissues too.