To reveal the variation patterns and driving mechanisms underlying leaf phenotypic diversity in Quercus mongolica and provide a data basis for constructing Quercus mongolica germplasm banks, breed suitable provenances, and to promote sustainable utilization.

Thirteen leaf phenotypic traits were systematically measured for 55 Quercus mongolica provenances from northeast and north China. Nested analysis of variance was used to quantify variation contributions among and within provenances; phenotypic differentiation coefficients were employed to analyze the degree of genetic differentiation; principal component analysis (PCA) and UPGMA clustering were combined to explore the classification value of traits; regression models were utilized to evaluate the impact of climatic differences (e.g., annual average temperature, seasonal rainfall) between provenance and planting sites on phenotypes.

All 13 traits show significant differences among provenances (P<0.05), with coefficients of variation (CV) ranging from 18.81% to 63.50%. Among them, leaf area (CV=63.50%), petiole length (45.42%), and leaf base angle (39.86%) exhibit the most significant variations. The average phenotypic differentiation coefficient is 61.99%, and the variance contribution among provenances (57.65%) is significantly higher than that within provenances (35.09%), indicating that variation mainly originates from geographical population differentiation. Correlation analysis shows that different leaf traits are mainly highly correlated with leaf length and leaf width. PCA extracts 3 principal components (cumulative contribution rate 66.60%), with dominant factors being leaf length (PC1 loading 0.954), leaf tip angle (PC2 loading 0.745), and leaf base angle (PC3 loading 0.743) in sequence. Cluster analysis divides the 55 provenances into 3 types: large-leaf type (6 provenances), medium-leaf type (23 provenances), and small-leaf type (25 provenances). The medium-leaf and small-leaf types account for 90.9%, with classification based on leaf size (leaf length, leaf width) and angle characteristics (leaf tip angle, leaf base angle). Climatic differences between provenance and planting sites have significant effects on 6 traits (P<0.05), but the explanatory rates (coefficient of determination, R²) are generally low (<0.17).

Leaf phenotypic diversity in Quercus mongolica is dominated by genetic differentiation among provenances. Leaf area, petiole length, leaf base angle, leaf perimeter, and leaf vein angle are key indicators of phenotypic differentiation; leaf length, leaf tip angle, and leaf base angle can serve as core indices for germplasm classification. Climatic factors have a weak impact on traits, indicating that genetic background is the main cause of variation.