Effects of Different Substrate Ratios on Growth and Physiological Characteristics of Container Seedlings of Quercus chenii

Quercuschenii Nakai is an ecologically and economically valuable tree species in China, but systematic research on container seedling cultivation is lacking. An optimal substrate mixture is critical for producing high-quality seedlings. A {4,3} simplex centroid mixture design was used to prepare 15 substrate mixtures combining peat, yellow subsoil, sawdust, and rice husk. Growth parameters, root morphology, biomass accumulation, and physiological indices of container seedlings were measured. Principal component analysis (PCA) and membership function method were applied for comprehensive evaluation, while substrate costs were also considered. Treatment T3 (20% peat + 80% yellow subsoil) produced the highest seedling height (59.3 cm), ground diameter (4.13 mm), total fresh weight (8.83 g), total dry weight (4.04 g), chlorophyll content (48.18 SPAD), soluble sugar (4.29 mg·g−1), and soluble protein (23.62 mg·g−1). PCA and membership function ranking showed T3 (0.88), T1 (100% yellow subsoil, 0.71), and T6 (60% peat + 40% yellow subsoil, 0.70) as the top three treatments. Bulk density of substrates ranged from 0.17 to 1.14 g·cm−3, and costs from 72.6 to 383.2 CNY·m−3. T3 had a bulk density of 0.89 g·cm−3 and cost 246.7 CNY·m−3, representing the best overall performance. The T3 mixture (20% peat + 80% yellow subsoil) provides moderate bulk density and cost, significantly promotes growth and physiological metabolism of Q. chenii seedlings, and is recommended as the optimal substrate for production.