Responses Of Eleven Ornamental Tree Species To Sulfur Dioxide Stress Treatment

Potted two-year-old seedlings of eleven ornamental tree species(Gleditsia sinensis Lam.,Fraxinus velutina Torr., Liriodendron chinense Sarg., Celtis sinensis Pers., Melia azedarach Linn., Koelreuteria Paniculata Laxm., Ligustrum lucidum Ait., Catalpa ovata G., Ailanthus altissima var. 'Hongye', Clerodendrum trichotomum Thunb., Aesculus chinensis Bunge) were fumigated by sulfur dioxide with different concentrations and different time treatment in a special designed fumigation equipment. The injured symptoms, membrane permeability, content of soluble protein and MDA, activities of SOD, POD and CAT, content of chlorophyll and carotenoid, gas exchange character parameters, content of sulfur in leaves, activity and absorption area of the root system, size and density of the stomata were tested. Responses and resistant mechanisms of the tree seedlings to sulfur dioxide were studied comprehensively on the basis of data analyses by mathematical methods such as correlation analysis, clustering analysis, main components analysis and subordination function method etc. The main results are as the followings. 1. Most tree species had the same injured symptom under long-time mild concentration or short-time severe concentration sulfur dioxide stress, which showed that resistance of each tree species to sulfur dioxide has a threshold value. 2. The plants reduced the intaking amount of sulfur dioxide entered by stomatal closing, so that the photosynthesis was influenced to some extent and on the other hand, because photosynthetic pigments were destroyed, the speed of the photosynthesis was reduced. Stomatal closure of the tree species had different trends as the increasing of sulfur dioxide concentration. For example, those of Aesculus chinensis Bunge and Ailanthus altissima var. 'Hongye'were closed first and then opened, and that of Fraxinus velutina Torr. was opened first and then closed. This is probably an adaptive mechanism to absorb more oxygen; the stomata of other tree species were closed gradually in order to reduce the oxygen intake, this might be a strategy of adaption to stress environments. 3. Chlorophyll in the leaves of each tree species was destroyed to different extend under the sulfur dioxide stress, and the severer the stress is, the higher degree of the chlorophll is. The content of carotenoid of Liriodendron chinense Sarg., Celtis sinensis Pers., Fraxinus velutina Torr.and Gleditsia sinensis Lam. appeared an increasing and then a decreasing trend as the increasing of sulfur dioxide concentration; that of Clerodendrum trichotomum Thunb., Melia azedarach Linn., Aesculus chinensis Bunge, Ailanthus altissima var. 'Hongye'and Catalpa ovata G. appeared a steady decreasing trend and that of Koelreuteria Paniculata Laxm. and Ligustrum lucidum Ait. appeared a steady increasing trend. 4. Both the increasing of sulfur dioxide concentration and the lengthening of sulfur dioxide stress treatment can increase the contents of MDA. The contents of MDA and electrolyte leakage were positively correlated. Contents of MDA and electrolyte leakage of resistant tree species under stress such as Aesculus chinensis Bunge, Ailanthus altissima var. 'Hongye', Celtis sinensis Pers., Fraxinus velutina Torr. were basically kept stable. Other tree species such as Ligustrum lucidum Ait., Catalpa ovata G. and Clerodendrum trichotomum Thunb. showed different changing trends, especially after 4-8 hours under sulfur dioxide stress. 5. Three protective enzymes (SOD,POD,CAT) in seedlings of Celtis sinensis Pers., Ailanthus altissima var. 'Hongye', Aesculus chinensis Bunge played an important role in resisting sulfur dioxide oxidation, but Gleditsiasinensis Lam., Ligustrum lucidum Ait., Catalpa ovata G., Liriodendron chinense Sarg. probably had other mechanisms to avoid sulfur dioxide injury. 6. Only under mild concentration of sulfur dioxide, can plant produce 'adversity protein'. High concentration of sulfur dioxide can destroy the protein severely, and therefore the plant was not able to produce protein. The protein in some high-resistant tree species such as Fraxinus velutina Torr., Celtis sinensis Pers., and Gleditsia sinensis Lam. at the initial stage of stress was destroyed to some extend, but they adapted to the stress condition gradually and produced 'adversity protein', so their resistant abilities were increased. 7. Difference in sulfur iron content among tree species at two different stress conditions reflected their relative ability to absorb sulfur dioxide. The order of this ability is as the followings from strong to weak: Ailanthus altissima var. 'Hongye'> Koelreuteria Paniculata Laxm.> Fraxinus velutina Torr.> Celtis sinensis Pers.> Gleditsia sinensis Lam.> Melia azedarach Linn.> Liriodendron chinense Sarg.> Aesculus chinensis Bunge> Clerodendrum trichotomum Thunb.> Ligustrum lucidum Ait.> Ligustrum lucidum Ait.. 8. Height growth increment of Aesculus chinensis Bunge, Ailanthus altissima var. 'Hongye', Melia azedarach Linn., Koelreuteria Paniculata Laxm., Fraxinus velutina Torr. are higher than that of the check, the others are lower than that of the check under 5.4mg·m-3 sulfur dioxide stress condition, this indicated that the resistant tree species have the compensation effect to overcome the adverse environment by accelerating growth. Height growth increment was closely related with the injured degree of each tree species. 9. Deoxidating intensity of nitroblue tetrazolium of root system of all tree species have two different changing trends: that of Fraxinus velutina Torr., Clerodendrum trichotomum Thunb., Koelreuteria Paniculata Laxm., Celtis sinensis Pers. were increased as the sulfur dioxide concentration increasing, their pollution resisting index was relatively higher; that of Liriodendron chinense Sarg. Melia azedarach Linn., Ligustrum lucidum Ait, .Catalpa ovata...