Seedling Stress Physiology Of Several Coniferous Species

Effects of water and heat stress treatments on Chlorophyll fluorescence (Fv/Fm),Gas exchange, Carbon isotope composition; Sugar contents ,seedling height and biomass of Chinese fir, Masson pine, Douglas fir ,western redcedar and lodgepole pine seedlings were measured during a three cycle stress period in spring 2001 at The University of British Columbia. And the effects of shoot pruning, root cutting, exposure to sunny field as well as freezing treatments on root growth potential, seedling survival rate, electrolyte conductivity and activity of dehydrogenase of 1-0 Chinese fir and Masson pine bareroot seedlings before planting were also conducted in spring 2000 at Nanjing Forestry University. The results were shown as follow: (1)Fv/Fm ratios of Chinese fir, Masson pine and western redcedar had different responses to water stress treatments. The Fv/Fm ratio of western redcedar decreased dramatically after water stress treatments while that of Chinese fir had only a slight reduction and that of Masson pine had no significant change. The experiment also showed that the Fv/Fm ratio of all three species differs significantly under heat stress treatments. Concerning three different water and heat stress cycles, it was found that the Fv/Fm ratios of Chinese fir and Masson pine measured at the end of each water and heat stress cycle was not significantly different. However, the Fv/Fm ratio of Western redcedar was diminished significantly in response to an increase of stress time. (2)After 36 days water stress treatments, the net photosynthesis of all three species including Chinese fir, Masson pine and Western rededar decreased significantly. But heat stress only affects the net photosynthesis of Chinese fir and Western redcedar. It was only be observed that the needle conductance to water vapor of Masson pine was significantly affected by both water and heat stress treatment. The needle conductance to water vapor of other species has just a slight change after water and heat stress treatment. Therefore, instantaneous water use efficiency, which was expressed as the ratio of A/ gwv, has no significant difference except for masson pine. (3)Different levels of water stress treatments in Chinese fir only slightly influenced seedling biomass. There is no significant difference in root dry weight under different level of water stress treatment. The biomass of Chinese fir, however, was dramatically affected under heat stress treatment. All four biomass indexes have significant difference under different levels of heat stress treatments. Masson pine, another subtropical tree species, showed significant difference in all biomass indexes under both water and heat stress treatment except for root/shoot ratio (dry weight) under heat stress treatments. Douglas fir showed that its four biomass indexes were significantly effected by heat stress treatment but not by water stress treatments. The western redcedar also showed that the heat stress influenced its biomass much stronger than water stress did. Lodgepole pine, had the similar trend to tolerate heat and water stress treatment as redcedar and Douglas fir. All its biomass indexes had no significant different under water stress treatments but there are differences observed under heat stress treatments. (4)There are significant differences in carbon isotope composition(δ(13)~C) among four species including Chinese fir, Masson pine, Douglas fir and Western redcedar under water stress treatments. Along with the prolong of water stress, the value of carbon isotope composition(δ13C) of all four species increased. This means that the Water Use Efficiency (WUE) will be improved under water stress treatments. Heat stress treatment had also significant effects on carbon isotope composition(δ13C) of Chinese fir and western redcedar. But the differences of carbon isotope composition(δ13C) did not be observed under heat stress in Masson pine and Douglas fir. (5)There is no significant difference of Fructose in Chinese fir needles under water and heat stress treatment. But it was observed that there are significant differences of Sucrose and Glucose in Chinese fir needles under water and heat stress and the value of Sucrose and Glucose was found to increase under water and heat stress. Water stress had significant effects on Sucrose and Glucose contents in Masson pine needles while heat stress had significant effects on Fructose and Glucose contents in Masson pine needles. And It was shown that All three sugars were found to increase under water and heat stress in Masson pine. (6)Both shoot pruning and root cutting treatments have a significant effects on root growth potential of Chinese fir and Masson pine , but the changing extent of root growth potential is different between two species. The results also showed that root growth potential of both species will decreased rapidly after exposure only a few hours to sunny field. We also carried out a correlation analysis between seedling morphological indexes and root growth potential and the results told us that most of morphological indexes of both species have significant relationship with root growth potential. Finally, The relationship analysis between seedling density and root growth potential showed no regular relationship between them. (7)Needle Electrolyte conductivity of Chinese fir and Masson pine has a big increase after freezing treatment and there are no significant differences of needle electrolyte conductivity between two species. The fine root activities of dehydrogenase of both Chinese fir and Masson pine are significantly correlated with the intensity of freezing and desiccation. We suggested that both electrolyte conductivity and activity of dehydrogenase could be used as quick indicators of Chinese fir and Masson pine bare-root seedling quality. (8) Root growth potential and field survival decreased along with prolonging duration of exposure. to sunny field. –1.60Mpa and –1.70Mpa are suggested critical values of Chinese fir and Masson pine respectively for successful reforestation.