Study On Selection And Evaluation Criteria Of Salinity Tolerance Tree Species In Coastal Region

In this study, two-year-old seedlings of 16 tree species grown in pots containing soils were subjected to salinity (NaCl) treatments in order to determine their salt tolerance. After 40 days of salt stress, we observed and measured 36 indicators related to salt tolerance, including the growth and morphological parameters, photosynthetic factors and chlorophyll fluorescence parameters, biomembrane systems, enzymic systems and abscisic acid, organic osmolytes and mineral elements. By subordinate function, principal components analysis and gray interacting analysis, 13 parameters were selected to evaluate efficiently the seedlings'salt tolerance, and the index system of evaluation and its standards for salt tolerance was also established. The main points of this current study were summarized as follows:1. With a single index or a single field of indexes, we can not accurately and completely evaluate the salt tolerance of various tree species. The more indicators selected, the more accurate evaluation will be obtained. The results may be considerably different if we use one of the five fields of parameters to separately evaluate the seedlings'ability to tolerate salt stress by subordinate function.2. By the method of subordinate function, the salt tolerance of 16 tree species was determined comprehensively, that is, Nitraria Sibirica > Nitraria tangutorum > Euonymus alatus (Thunb.)Sieb.> Tamarix chinensis Lour.> Salix psammophila > Celtis laevigata > Ligustrum obtusifolium.> Rhamnus cathartica L.> Gleditsia triacanthos > Elaeagnus angustifolia L. > Lonicera tatarica L.> Fraxinus americana > Salix > Pvrus betulaefolia Bunge > Buddleja lindleyana Fort. > Cephalanthus occidentalis.3. Based on the results of salt-damaged symptoms and salt-tolerant sequence evaluated from subordinate function, the 16 tree species were divided into three salt-tolerance levels. The principal component analysis showed that, at different levels, the indices which play a key role in salt-tolerance evaluation may be different. For the plants with low salt-tolerance level, the main indicators are growth and morphological parameters, organic osmolytes and various mineral elements, while for the plants with high level of salt tolerance, the key indicators are growth and morphological parameters, bio-membrane systems, organic osmolytes and some inorganic ions, such as Na~+, K~+ and Cl~-. 4. Based on the results of principal component analysis, 18 indicators related intimately with salt tolerance were screened out. The correlation coefficients between them and subordinate function were calculated by gray relational analysis, subsequently sorted, and finally made the determinant parameters involved in salt-tolerance evaluation, which are Cl~-, Na~+ and K~+ content in stems, Cl~- and Na~+ content in leaves, Cl~-, Na~+ and K~+ content and K~+/Na~+ values in roots, proline content, betaine content, soluble sugar content and height growth, so the basic evaluation standards system was further determined. Based on the results mentioned above, the order of salt tolerance of 16 tree species from high to low was: Nitraria Sibirica > Nitraria tangutorum >Tamarix chinensis Lour. > Euonymus alatus (Thunb.)Sieb.>Salix psammophila >Ligustrum obtusifolium.> Elaeagnus angustifolia L.> Buddleja lindleyana Fort.> Rhamnus cathartica L. > Lonicera tatarica L.> Celtis laevigata > Gleditsia triacanthos > Cephalanthus occidentalis> Salix > Fraxinus americana > Pvrus betulaefolia Bunge.