| Saline soil is one of the important factors in restricting agricultural production and improving living environment. With rapid growth of the population and the high-speed development of economic construction, exploitation and utilization of saline soil, collecting salt-tolerant plants resources and mastering the plant salt resistance physiology and mechanism has become one of the important tasks of researchers.Considering the shortage of tree species for landscaping on the Tianjin coastal saline-alkaline land, I used the method of field investigation and control experiment to select some salt-tolerant plants for the coastal area. And indexes of salinity tolerance assessment applying to production practice were studied,in order to enrich green plant resources in the coastal area and improve the ecological environment.The main results are as follows.1,Beacause of higher soil salinity and less human intervention,the plant species were rich in the investigation site in Tianjin Tanggu Area Dagang reservoir,with the total species of 56 under 25 families. Graminceae and Chenopodiaceae families are the important constructive and dominant species of Saline soil, followed by Leguminosae, Rosaceae and Compositae. Special salt-tolerant plants included Tamarix chinensis, Apocynum venetum and so on, about 23.2% of total. Strong salt-tolerant plants indluded Fraxinus chinensis, Kochia scoparia and so on, about 16.1% of total. There were the largest number of Grass communities and a few Woody community, but distribution of pewter and tamarix community was large. In addition,the region was rich in wild and local salt-tolerant plant resources,for example Suaeda salsa,Phragmites communis,Fraxinus chinensis,Ziziphus jujube and so on.2,Based on the vegetation investigation of the coastal saline-alkaline soils in Tianjin Tanggu Area Dagang reservoir,combined with common greening plants in Tianjin, The 11 tree species grown in pots have been studied on the growth,morphological,physiological and biochemical characters under different concentration NaCl stress. Through measuring the indexes of salt resistant capacity, it was concluded that Sabina chinensis cv. Kaizuka was special salt-tolerant plant, Buxus sinica, Buxus microphylla var.koreana and Phlox drummondii were strong salt-tolerant plants, Weigela florida cv. Red Prince, Petunia hybrida, Ligustrum vicaryi, Caryopteris clandonensis and Syzygium aromaticum were moderate salt-tolerant plants, Ligustrum quihoui and Pinus×euramericana cv.'74/76' were mild or no salt-tolerant plants.3,Indicators such as the survival capability,the symptoms of the leaves,the height,the biomass, the moisture content,the content of Pro and MDA,the content and the selective transportation of Na+,K+ Ca2+,Mg2+ were changing during the different stress period and the stress symptoms. A combination of growth rate and physiology indexes could be used for reflection of tree species salt-tolerant.The salt damage index of leaves of 11 tree species rise, at the same time, the height, the biomass and water content were inhibited and the difference among NaCl concentration were more significant with the stress time. Under 0.6% NaCl stress, the Moisture Content of Ligustrum quihoui and Pinus×euramericana cv.'74/76' reduced 19.82% and 13.90% over that of control in the experiment, however, Sabina chinensis cv. Kaizuka and Buxus sinica reduced only 7.18% and 7.73%. They two showed strong containing salt ability.The electrolyte leakage and the content of Pro increased and the difference was significant.To most tree species, the trends of the content of MDA were not obvious. Na+ content increased under the stress of NaCl in most species within the organization. The changing trends of K+ content was opposite to Na+.Ca2+ content was difference among these species, bsically unchanged in salt tolerance plants while decreased in salt-sensitive plants,the same as Mg2+ content. However,there were differences among the species in response time and concentration.The indexes changed slowly in salt stress endure range,but change was dramatic beyond the critical point.The differences had to do with Species characteristic and stress tolerance range.Pro could protect the cell membrane and reduce the damage of salt,and therefore insure plant growth. Nevertheless, Pro could not disarm injury from MDA to cells.4,It was difficult to accurately reflect the strength of salt resistance only on one single character or an index of analytical results. It was necessary to use multiple indices in evaluating salt tolerance so that the result had veracity and reliability.Each factors in salt stress played the different part and importance. On the whole, three analytical indices could mostly reflect salt tolerent which included the salt damage of leaves, the electrolyte leakage and the content of Pro.If only simply to determine or compare salt tolerent among plants in production practice, we tend to use the morphological indexes which could be observed easily.meanwhile the electrolyte leakage as a physiological target was choosed because of steadiness and easy measure.The results not only afforded several suitable landscape plants for the coastal areas, but also help to provide the theoretical and technical support for selection of salt-tolerant tree species and evaluation indexes.
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