Photosynthetic Physiological Characteristics of Tetracentron sinense Oliv in Different DBH Classes and the Factors Restricting Regeneration

Tetracentron sinense is an endangered tree species mainly distributed in Western China. In natural population of T. sinense, fewer young individuals and their concentration in the forest understory, whereas middle-aged individuals gradually transited from the understory to the forest gap and edge habitats, resulting in poverty natural population regeneration. Individuals from different age classes of T. sinense may differ in their photosynthetic adaptability to the different light conditions in the understory, forest gaps and forest edges. Whether these differences are the main factors limiting the natural regeneration of this species remains unclear. This study aims at elucidate the changes in photosynthetic physiological characteristics with age, and discuss the effective conservation and management strategies for this species. We used the Li-6400XT photosynthetic analyzer to examine the photosynthesis characteristics (including P_n-PAR, P_n-CO₂ and SLA) of T. sinense individuals of different diameters at breast height (DBH) classes, and analyzed the different DBH individuals' differences in photosynthetic and physiological. The results showed that the photosynthetic adaptability of T. sinense to a light environment would be different throughout the life cycle. The ability to adapt to the light environment, CO₂ utilization potential and accumulation of photosynthetic substances was significantly higher in the reproductive initiation stage of T. sinense than other stages. T. sinense individuals' environmental adaptability in the pre-reproductive stage was relatively weak, which may be one of the main factors limiting natural regeneration. Therefore, the area of forest gaps in T. sinense natural populations should be expanded by artificial interference to facilitate the growth of young individuals and promote population regeneration.