Abstract: We studied the response of photosynthetic physiological characteristics of three poplar clone seedlings to NaCl stress with three kinds of poplar(Populus L.) clones of poplar(Populus L.) clone seedlings including ‘A5’(Populus pseudo-simonii×P.nigra)×(P.simonii×P.nigra), ‘J7’(P.deltoidis×P.catyana CL.‘J7’) and ‘1344’(P.deltoids×P.cathayana CL.‘1344’) in Heilongjiang Province. Three NaCl stress treatments were established at the contents of 0.3%, 0.5% and 0.7% (percentage of NaCl in total dry soil mass). The salt injury symptoms first appeared in ‘1344’ under NaCl stress, followed by ‘J7’ and ‘A5’. Furthermore, under the same NaCl content, the maximum damage due to NaCl stress also occurred first in ‘1344’, followed by ‘J7’ and ‘A5’. The mean tree diameter at breast height and total tree height differed signi?cantly under three NaCl stress treatments. Moreover, the difference between three NaCl stress treatments gradually become bigger, which was 10%-35% lower than the control treatment during the late period of this experiment. With the increase of NaCl, the chlorophyll content decreased, with the decrease in ‘J7’ being much more obvious than in ‘A5’ and ‘1344’. With the increase of NaCl, the content of carotenoid in ‘A5’ increased, and ‘J7’ and ‘1344’ decreased. Chlorophyll b content under 0.3% NaCl stress in ‘A5’ and ‘1344’ was higher than that in the control, while the ‘A5’ chlorophyll b content under the 0.5% and 0.7% NaCl stress levels were in contrast not significantly different, but ‘1344’ under 0.3% and 0.5% NaCl stress levels was significantly higher than that in the control and the 0.7% NaCl stress level. ‘J7’ showed no significant difference when compared with the 0.3% NaCl stress, but was higher than the 0.5% and 0.7% levels. The photosynthesis of the clone seedlings reduced due to the NaCl stress. The G_s and C_i of the leaves decreased with the increase of the salt, while the L_s mainly decreased. One possible explanation for the phenomenon in this study may be that the photosynthetic physiology was greatly influenced by stomatal limitation and non-stomatal limitation. The WUE of three poplar seedlings under NaCl was maintained at a higher level, which may suggest that these poplar seedlings have a strong resistance to NaCl stress. Therefore, ‘A5’ had the strongest salt-tolerant ability among these three clones.

Key words: poplar clones, NaCl stress, growth, photosynthesis