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Comparison of Osmotic Adjustment and Ion Balance Strategies of Eleven Alkali-tolerant Halophytes During Adaptation to Salt-alkalinized Habitats

Author: LiuZhaoXia
Tutor: ShiDeCheng
School: Northeast Normal University
Course: Botany
Keywords: halophyte salt-alkalinized habitats osmotic adjustment ion balance
CLC: Q945.78
Type: Master's thesis
Year: 2011
Downloads: 58
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Abstract


The salinization of soil is a widespread environmental problem and an important factor in limiting agricultural productivity. According to the difference of salt components in soil, salinized soil can be divided into saline soil and alkaline soil. The saline soil contains only neutral salts NaCl and Na2SO4, the alkaline soil contains not only neutral salts but also alkaline salts NaHCO3 and Na2CO3. However, in natural conditions, salinization and alkalization frequently co-occur. For example, the alkalinized grassland in northeast China is salt-alkaline mixed soil. These halophytes live for extended periods on semiarid alkalinized grassland, they need to cope with not only salt and drought stresses but also high-pH stress. The halophytes in this area have formed unique physiological mechanism in order to adapt to salt-alkalinized habitats. Consequently, further study on physiological mechanisms of these halophytes is helpful to selection and cultivation of new halophytes.In the present study, 11 halophyte species growing on semiarid alkalinized grassland of northeast China were chosen as test species, including three species of Poaceae, five of Leguminosae, one Asclepiadaceae, one Cyperaceae, and one Boraginaceae. In addition, the soil surrounding each species of plant roots was collected. The soil samples were used to determine pH and electrical conductivity. Physiological indices of 11 halophytes were measured, including the contents of free inorganic ions and organic acid (OA). Finally, their osmotic adjustment and ion balance strategies to the salt-alkalinized habitats were compared.The results of 11 halophytes indicated that there were a lot of in common and a diversity in their osmotic adjustment and ion balance strategies. The comparisons can be made from two aspects. Firstly, in this experiment, all halophytes accumulated betaine and soluble sugar (SS) as dominant organic osmolytes in protoplasm, and accumulated Na+, Cl– and OA as the main osmolytes in vacuoles. In all the species, the osmotic contributions of both proline and free amino acid (AA) were very small. Although Na+, K+, Cl– and OAs were the main osmolytes in vacuoles for most species, their contributions to osmotic adjustment were different. Secondly, ion imbalance of plants under salt stress is mainly caused by the influx of superfluous Na+. Under saline conditions, halophytes usually accumulate inorganic anions or synthesized organic acid, to neutralize massive positive charges and maintain intracellular ion balance. The results showed that inorganic anions and OAs might have different roles in various halophytes. The dominant intracellular cations in all halophytes were Na+ and K+, while both contributions to ion balance were different among the species. For most species, OAs and Cl– were the dominant anions in maintaining ion balance. In some species such as all Poaceae, the contributions of Cl to total anion were higher than that of OAs. However, in species such as all Leguminosae , Cynanchum chinense and Carex duriuscula OAs was the dominant factor in maintaining ion balance. In addition, in several species, such as Messerschmidia sibirica, SO42– was also important in ion balance.

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