离子吸收分布与几种荒漠植物适应性的关系

Ion uptake and distribution in relation to the adaptability of several desert species

用压力室灌流挤压法结合原子吸收分光光度计测定了胡杨、沙枣、柽柳、梭梭和花棒等5种荒漠优势植物组织以及细胞内和质外体溶液中K+、Na+含量,并用TPS-1型光合蒸腾测定系统和露点微伏压计测定了叶片(同化枝)的蒸腾速率和组织渗透势,以分析荒漠植物离子吸收特点与其适应性的关系。结果表明:5种植物叶片(同化枝)中K+含量差异较小,但Na+含量却有极显著差异,其中梭梭Na+含量最高、胡杨和柽柳次之、花棒和沙枣相对较低,且梭梭和柽柳的根系和组织细胞膜对Na+也具有更高的透性。另外,实验结果还显示组织Na+含量与组织渗透势和蒸腾失水率均呈显著负相关,即Na+的吸收、积累可能在渗透调节和减少水分散失中具有重要作用。由此可见,梭梭和柽柳能够通过大量吸收和积累无机离子来降低渗透势、增强吸水力,同时减少蒸腾失水,具有很强的荒漠环境适应能力;而胡杨蒸腾耗水量较大、花棒和沙枣生理吸水的动力不足,与梭梭和柽柳相比,其荒漠环境适应能力相对较弱。

Because the evaporational water loss is far beyond the water supply by rainfall in desert areas,desert plants often suffer from simultaneous drought and saline stresses.Under desert conditions,the increase in ion concentration in soil solution forces the plants to take more salt due to the elevated salt concentration gradient between the soil solution and the solution in root xylem on the one hand,and makes the absorption of water more difficult for plants on the other.So the different features in salt absorption in different desert plants may be closely associated with their drought adaptability.It is in this sense that the study of the ion absorption feature in desert plants are important in understanding the desert adaptability of plants.However,little attention has been paid to this issue up to now.In this study,the capability of adapting to desert environment in 5 desert plants in terms of their ion absorption,transportation and redistribution was investigated with modified liquid perfusion technique with the aid of a pressure bomb.The experiments involve the measurement of K ＋ and Na ＋ content in solutions of cells and intercellular spaces in 5 typical desert plants,namely Populus euphratica Oliv.,Elaeagnus angustifolia L.,Tamarix chinensis Lour.,Haloxylon ammodendron（C.A.Mey.） Bunge and Hedysarum scoparium Fisch.with an atomic spectrophotometer,the solutions of cells and intercellular spaces were collected with pressure perfusion method,in which the solutions perfused into plant tissues were pressed out with the pressure bomb and the ion content in solutions was then analysed.In parallel to the ion content measurements,the transpiration and tissue osmotic potential were measured with a TPS-1 photosynthesis system（PP systems,UK） and an HR-33 vapour pressure osmometer（Wescor Inc.USA）,respectively,in order to analyse the feature of ion absorption in desert plants and its relation to desert adaptability.The results showed that the difference in K ＋ content in the measured species was not significant,but the difference in Na ＋ content was very significant.H.ammodendron showed the highest Na ＋ content,followed by P.euphratica,T.chinensis,H.scoparium and E.angustifolia having the lowest Na ＋ content.Accordingly,the cell membrane in H.ammodendron and T.chinensis exhibited higher permeability to Na ＋.Additionally,the experiments showed that both the tissue Na ＋ content and tissue osmotic potential was negatively correlated to the transpiration rate of the plants,implying that the Na ＋ absorption and accumulation may have played an important role in reducing and regulating the water loss in plants.It is therefore concluded that H.ammodendron and T.chinensis can lower their tissue osmotic potential and enhance the driving force for water absorption,at the same time reduce their transpirational water loss by morphological modifications and physiological adaptations,thus was able to retain a high adaptability to desert.On the other hand,due to higher transpirational water dissipation in P.euphratica,and due to smaller driving force for water absorption in H.scoparium and E.angustifolia,the adaptability to desert environment in these three plants is lower compared with that in H.ammodendron and T.chinensis.