Study On Saline-alkali Tolerance Of Seeds And Seedlings Of Fraxinus Velutina Torr.

The potted one-year-old seedlings and seed of chinese ash were tested to study their response to neutral salt and salt-alkali mixed stresses. The germination,growth, physiological and biochemical indexes were measured to study their responses to neutral salt stresses and akaline salt stresses and the intercross stress of salt and alkali. The main results are as the followings:The germination capability of chinese ash was restrained obviously under neutral salt and alkaline salt stresses. Complex saline-alkali stress decreased germination rate, germination energy, germination index and vigor index, with an increased saline-alkali concentrations, the trend became more obvious .The mix effect of high saline-alkali stress was much stronger than high salt stress or high alkali stress .The activity of SOD appeared an increasing trend as a whole, the activity of CAT appeared an increasing trend.The height growth of seedlings was inhibited and the biomass was decreased under the neutral salt and alkaline salt stresses. Under different stress level, the ratio of root to stem was increased significantly; Adding nutrients distribution to root may be the main adapting stress way of chinese ash.Under neutral salt stress , the cell membrane osmasis and MDA contents of chinese ash cell were increased, At early stage of alkaline salt stresses , the cell osmasis membrane appeared an declining and then increasing trend, MDA was increased as a whole , the correlation analysis indicated that the membrane lipid peroxidation of leaves was the main factor to the damage of the cell structure and function.At the early stage of neutral salt stress, the activities of SOD, POD, and CAT were increased and the damage of free radical were off set. At later stage of the stresses, the decreasing of SOD, POD, CAT activities indicated that the capcity of eliminating free radical was weakening. The changes of SOD, POD, and CAT were very complex under alkaline salt stresses, it were not presented a single tendency .Under neutral salt stress ,the results showed that the contend of Chlorophyll a,a/b and Chlorophyll of Chinese Ash leaves appeared an increasing and then declining trend, The change of Chlorophyll b was not obvious. The Chlorophyll a were declining under salt and saline mixed stresses, Chlorophyll b appeared an declining trend. No uniform trend in the change of Chlorophyll a/b and it was very complex. Both neutral salt and alkaline salt stresses can promote the contend of carotenoid.Neutral salt stress increased the contents of proline significantly, the contents of soluble sugar and soluble protein appeared an declining and then increasing trend, The contend of proline was not obvious under alkaline salt stresses, and the trend kept smooth, The reason might be the alkali neutralize some acid. The contents of soluble protein were increased and the increasing trend was more obviously under the salt and alkali stresses, it might be the adaptation of chinese ash for salt and alkali stresses. The change of soluble sugar was very complex.Under neutral salt stress and alkaline salt stresses, the characteristics of Na+ and K+ distribution were as followings: root>stem>leaf, leaf>stem>root, this indicated that root and stem accumulated lots of Na+ ions and affected the transportation of Na+ from stem to leaf. This way prevented leaves of chinese ash from Na+ damage and was a main way to promote the seedling adaptability to salt and alkali stress. Under neutral salt stress, the increasing of RS value were showed the selective transportation of K+ from root to stem and leaf was indeed a reason for the salt resistance of chinese ash, and the RS value appeared an increasing and then declining trend under alkaline salt stressesThe stomata limitation of photosynthesis was the main limited factor of chinese ash in the initial stage of neutral stress; the non-stomata limitation was the main limited factor of photosynthesis as following. under alkaline salt stresses , the stomata limitation was the main limited factor of photosynthesis.The injured extent of chinese ash eedlings under salt and alkali stress were compared by Subordination function method and the descending order was as following: D4>C4>E3>D2>B1>A1>A4>D1>E1>E2>B3>B4>D3>A2>C3>C1>A3>C2>B2。Results revealed that alkali salt stress and salt stress were actually two distinct kinds of stresses .The former was better called alkali stress, while salt stress only meant neutral salt stress. An interactive effect between salt stresses and alkali stresses could be found under mixed salt and alkali stress.