Photosynthetic characteristics of Dahurian larch, Scotch pine and white birch seedlings native to Eastern Siberia raised under elevated CO2.

Growth pattern and biomass production of trees will be affected by increasing atmospheric CO 2 , which may change the vegetation pattern in eastern Siberian where continuous permafrost is present.In this phytotron experiment, effects of enriched CO 2 on the shoot growth and photosynthetic parameters were examined to predict future regeneration capacity of major tree species in the permafrost region.The leader shoot of larch and white birch ceased to grow at 80-90 days after leaf unfolding, by contrast, Scotch pine stopped to shoot elongation at ca. 35 days.Growth cessation of seedlings raised under 70 PaC0 2 (high CO 2 ) was one week later as compared to seedlings grown under 36 PaC0 2 (ambient CO 2 ), Leaf area of white birch raised under high CO 2 was smaller than that at ambient CO 2 , while there was no difference in needle size of larch and Scotch pine grown under both CO 2 levels.Specific leaf area (SLA) deceased in all species raised under elevated CO 2 , There was no significant difference in the photosynthetic rate of the two conifers grown at high and ambient CO 2 levels.The photosynthetic rate in white birch measured at the growth CO 2 level showed almost the same value, which was considered as homeostatic adjustment.The apparent quantum yield and carboxylation efficiency of larch and white birch raised under high CO 2 decreased, while those of Scotch pine showed no difference.Instantaneous value of water use and nitrogen use efficiency in all seedlings raised in enriched CO 2 increased especially for Scotch pine.Based on these results, we infer that, in a future elevated CO 2 condition, the larger increase in water use efficiency of Scotch pine could enhance its dominance the forest of eastern Siberia region.