Coordination and Variation of Photosynthetic Pigments Across Seedling Ages and Grades Reveal Adaptive Strategies in Pinus yunnanensis

Pinus yunnanensis is a vital native species for afforestation in Southwest China, and seedling quality determines restoration outcomes. Seedling grading is widely applied to select robust seedlings, whereas physiological distinctions among seedlings of different grades remain unclear. In the present study, allometric scaling, coefficient-of-variation calculation and correlation analysis are adopted to investigate pigment traits and resource-allocation characteristics of Grade I, Grade II and Grade III seedlings across successive developmental stages. Seedling grade and seedling age exert significant influences on photosynthetic pigment traits. Grade I seedlings exhibit stable pigment composition, steady allometric growth and strong phenotypic stability, with key physiological transitions taking place at 330 d and 510 d. Chlorophyll b showed the highest trait variability. The present results verify the superior adaptability of Grade I seedlings and provide theoretical support for early seedling-quality evaluation and precise seedling cultivation.