Abstract: Aimed to understand the responses of the dominant tree species (Pinus koraiensis, Picea koraiensis, Juglans mandshurica, Fraxinus mandschurica, Phellodendron amurense) in the secondary forests of Northeast China to the variations of light intensity, their seedlings or saplings were grown under different light intensities (15%, 30%, 60%, and full irradiance), with their specific leaf area (SLA) measured. The SLA was species-dependent, and there was a significant difference between evergreen coniferous species and deciduous broadleaved species ( P <0.001), suggesting the different life strategies between the two functional groups. With the decrease of light intensity, the SLA of test tree species had an increasing trend, especially at 15% and 30% irradiance compared with at 60% and full irradiance ( P <0.05). There was a large inter-specific variability in the SLA flexibility with respect to light intensity. In addition, the light regimes where the largest variations of SLA occurred were distinctly different. The SLA of  P. koraiensis  with different ages exhibited the similar variation pattern with light, whereas higher flexibility was observed in relatively young seedlings (4 years old). It was suggested that all test tree species could adapt to the variations of light condition by changing their leaf morphology. At low light conditions, the seedlings would increase their light resource capture ability by enlarging leaf area per unit mass. However, species-dependent responses to light implied the differences in light acclimation mechanisms, which would be very important for the co-existing of different species in forest ecosystem. The greater responses of younger seedlings to light indicated the important role of the seedlings in the study of leaf level eco-physiological mechanism during plant regeneration.

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