Response Features Of Four Tree Species Such As Fraxinus Velutina Torr. To Salt Stress Treatments

In this study,①Fraxinus velutina (Fraxinus velutina Torr.)Clone No. R36,②Salix (Salix gordejevii Chang et SKV),③Safflower honeysuckle (Lonicera japonica Thunb),④Gold leaf Caryopteris (Caryopteris clandonensis 'Worcester Gold') are the four annual seedling tree species for the material. In order to understand their salt tolerance mechanisms, we studied their physiological and biochemical responses to salt stress. As randomized complete block experiment was designed, 0‰(CK), 2‰, 3‰, 4‰, 5‰and 6‰six different gradients of soil salinity levels were prepared and measurant was made each on June 12, June 19, June 26, July 3 and July 10. Symptoms, cell membrane permeability, MDA, proline, soluble sugar, soluble protein, SOD, chlorophyll and other indexes were tested. After destruction of sampling, Na +, K +, Cl- contents and root activity were measured. Principal component analysis, multiple comparisons, correlation analysis, and other mathematical methods were employed to evaluate the salt resistance size of four tree species. The aim is to study the response characteristics of four tree species and understand the mechanism of woody plants under salt stress.First of all, in order to get the required six salt gradients of the soil salt contents, pre-tests were conducted. Determined by simulation of the soil of salt contents preparation test: 3.0‰salt water irrigating soil obtained 2.06‰soil salinity; 4.5‰salt water irrigating soil obtained 3.18‰soil salinity; 7.0‰salt water irrigating soil obtained 4.16‰soil salinity; 8.0‰salt water irrigating soil obtained 5.00‰soil salinity; 9.5‰salt water irrigating soil obtained 5.92‰soil salinity. In order to ensure continuity of the test, it is rough measured salt content directly using wet soil, and test results showed that there was a little difference between the natural dried soil and wet soil from salt pond.The extent of inhibition and the leaf symptoms of the four tree species seedlings under salt stress could reflect the differences of salt tolerance: Fraxinus velutina > Salix> Gold leaf Caryopteris> Safflower honeysuckle.Cell membrane permeability under salt stress increased with the salt treatment, and chlorophyll decomposition accelerated, and root activity and net photosynthetic rate declined. With time of salt stress, the declining extent of these indicators also increased. SOD, soluble sugar, soluble protein did not exhibit a single trend. And with the salt stress time, between most of the indexes are significant differences.Integrated four species, Pro variation of gold leaf Caryopteris is largest under salt stress, ash followed, Salix, and safflower honeysuckle minimum. Based on contents of Pro under salt stress torlerance, the salt-resistant of those four tree species showed that: gold leaf Caryopteris> Ash> Salix, safflower honeysuckle.Under salt stress, roots have maximum contents of Na+ and stems second, leaves at least. Leaf is the main part of plant damage. Roots and stems of Salix and Fraxinus velutina may be the major parts, which might be affected by salt. Plants can use these accumulated Na+ in the root to conduct osmoregulation, help reduce the plant water potential, maintain the capacity of plants absorbing water and preventing physiological drought. Ion content in leaves is low, the reason may be that roots and stems have accumulated a large amount of ions, and the ion upward transport are limited, which reduces salt stress on theshoots. The measured ion concentration of stem anatomy showed that Na +, K +, Cl- contents remained unchanged in xylem, indicating that the transfer and transport of ions carried out mainly in the phloem. The Cl- contents of the four tree species had no significant changes. Safflower honeysuckles are all dead under 5‰and 6‰salt stress gradient, which may be due to accumulate a large number of Cl- in stems and roots. Therefore the plants showed toxic symptoms.All of cell membrane permeability, chlorophyll, root activity, Pn, Gs, Tr were closely related to salt resistance of seedings.However those indexes can not be singlely used to evaluate species salt resistance.Comprehensive evaluation of salt resistance need much more information.It is difficult to accurately reflect the degree of salt tolerance of varieties, such as soluble sugar, soluble protein, Ci, etal. to be comprehensive evaluation of multiple physiological traits to only use a trait or an indicator of the measurements. This comprehensive evaluation of the degree of salt tolerance of species is accurate and reliable. It is a more accurate method to use stress symptoms and other indicators of field and cell membrane permeability, SOD, Na+, K+, Cl- ion contents to evaluate the combination of seedling salt resistance.Because of different species, different time and different salt stress, SOD activity was better able to explain the salt tolerance of plants which are controlled by many genes of a number of shapes that determines the complexity of the mechanism of salt.Through the correlation analysis of each index available, soluble protein can be used as the more reliable indicator of salt tolerance of safflower honeysuckle; MDA, Pn, and Cl- can be used as the more reliable indicator of salt tolerance of Salix; MDA , Pn and Tr can be used as a more reliable assessment of salt tolerance index of Fraxinus velutina; gold leaf Caryopteris had complex relationship between the various indicators, so the establishment of salt indicator system also needs deeper study.