| Salinisation is the important abiotic stress factor in restricting plant growth and reducing productivity. It has a significant meaning in remoulding saline-alkali land and improving economic returns by means of selecting highly salt-tolerant varieties to afforest on salination land. Poplars have the characters of fast growth, well-adapted, fine-texture, among them, which possessing the genome componential of Populus euphratica, have a strong ability of salt tolerance and may be used as the pioneer species in improving of saline land. Cutting seedlings of XH-1, XH-2 and LH-1 were used. And salt stress experiment was also carried out in pot. We had studied the morphology of salt damage and character of cytology, and revealed the regularity of morphological and physiological indexes. Principal component analysis and subordinate function analysis were also utilized to evaluate the salt tolerance. All these results provided a theoretical foundation in screening out the high salt-tolerant P. simonii×P. euphratica in the next work. The results showed as follow:(1) The salt damage degree could judged from the location and symptom of affected foliages. Along with the increasing of salt concentration and prolonging of stress time, the injury degree was more and more serious for P. simonii×P. euphratica. The base of seedling was firstly turned yellow, then it spread upward little by little. When there was a serious salt damage, foliage changed brownness and fell off, and even the stem got hurt and changed black brown for some seedlings. Visual symptoms of salt damage occured firstly, for LH-1, and the degree of it was the most serious. Visual symptoms of salt damage for XH-2 occured lastly, and the degree of it was the most lightest. However, for XH-1, the salt damage condition was between them. Therefore, according to the character of salt damage, XH-2 has the best salt tolerance, then the XH-1, while, LH-1 has a poor salt tolerance.(2) Foliage structure and inner organelles were different suffered for P. simonii×P. euphratica under a long time salt stress. With the increasing of salt concentration, volume was enlarged and number was increased gradually for mesophyll cell. The palisade tissue and spongy tissue both were tightly arranged, and their lengthes were elongated. The chloroplasts were gradually melted. The length of palisade tissue cell was longer for XH-1 and XH-2 than LH-1. Big vacuole was resolved into many little small ones, and they were completely obliterated as time went by. Structure of chloroplast was badly destroyed, and the inclusions were laid scattered in cell. Starch grains were incremental as the forming of score break.(3) Although the growth characteristic was not good as LH-1 for XH-1 and XH-2, but their salt-tolerant characteristic was superior to LH-1. Seedling height, ground diameter, root biomass, stem biomass, foliage biomass, whole plant biomass, foliage moisture content, stoma length, stoma width and foliage thickness were all affected by the interaction effect of variety and NaCl concentration. These data, excepting foliage moisture content, stoma length and foliage thickness, for LH-1, were higher than that of XH-1 and XH-2. And it was dropped off along with the adding of salt. Moreover, these indexes were little affected for XH-1 and XH-2. Foliage moisture content and foliage thickness, for XH-1 and XH-2, were significantly positive correlation, and increased with the adding of salt concentration. Root shoot ratio rose at first and then decreased with the increase of salt concentration.(4) Physiological indexes could sensitively reflect the salt stress situation for P. simonii×P. euphratica. With the increasing of salt concentration and prolonging of stress time, foliage Pro content and REC were went up, while, POD activity and relative chlorophyll content were reduced. The change regularity of MDA content wasn’t the same for the three varieties of P. simonii x P. euphratica. With the increasing of salt concentration and Prolonging of stress time, MDA content of LH-1 was rose, and that for XH-1 and XH-2 presented a fluctuated form of increase-reduction-increase.(5) The ability of ion selective absorption and transportation was closely related to their salt tolerance for P. simonii×P. euphratica. Na+content of root, stem and foliage were accumulated following the rising of salt concentration for three varieties of P. simonii×P. euphratica. K+content of root, stem and foliage were all affected by the interaction effect of variety and NaCl concentration. K+ content in foliage was higher than that of root and stem. Furthermore, K+ content of stem and foliage were accumulated with the increasing salt concentration for XH-1 and LH-1, whereas, K+ content of root was reduced. In addition, for XH-2, K+ content of stem and foliage changed slightly, and it of root was gained following the increased salt concentration. Variety and NaCl concentration only had a significant effect on Cl- content of foliage. With the rising salt concentration, the whole plant K+/Na+ ratio, root SK,Na and foliage SK,Na were decreased, nonetheless, stem SK,Na was went up gradually.(6) According to the results of morphology of salt damage, morphological and physiological indexes, and comprehensive analysis of salt resistance, we draw the conclusions that the salt-tolerant order of the three varieties was XH-2>XH-1>LH-1. |
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