Leaf Traits, Yield Components, and Seed Quality of Paeonia ostii Across Contrasting Understory Positions in a Pecan-Based Agroforestry System

To evaluate trait variation across contrasting understory light environments in a pecan-based agroforestry system, 30 seven-year-old Paeonia ostii plants were assessed at three naturally occurring positions with high (HI), medium (MI), and low (LI) understory light intensity. Microenvironmental conditions, plant growth, leaf photosynthetic pigments and mineral nutrients, seed yield components, seed oil traits, and final germination percentage were measured. Photosynthetically active radiation consistently followed the order HI > MI > LI. Plants at LI had higher chlorophyll a, chlorophyll b, carotenoid, and leaf N, P, and K concentrations, indicating leaf-level responses to lower light availability. In contrast, plant height and crown width were lower at LI, while HI showed higher values for 100-seed weight, aggregate fruit number and fresh weight, seeds per plant, and final germination percentage. Ground diameter and seed diameter did not differ significantly among positions. Crude fat and α-linolenic acid contents also showed no significant differences. Integrated trait analysis further showed that HI was associated mainly with higher growth, reproductive, and germination traits, whereas LI was associated with higher leaf pigment and mineral nutrient concentrations. Overall, the results reveal contrasting leaf-level acclimation and whole-plant performance across a naturally occurring understory PAR gradient. Because the study was observational, these patterns should be interpreted as position-associated differences rather than causal effects of light, and they provide a basis for future replicated canopy-management experiments.