Abstract: Investigating the effects of shading on the growth of Firmiana danxiaensis seedling during ex-situ reintroduction and evaluating comprehensive seedling quality will provide scientific evidence for the ex-situ conservation. With F. danxiaensis seedlings from afforestation, we conducted a single-factor experiment with different treatments including open space (CK), shading on all sides (S₁), shading on the west side (S₂), shading on the east side (S₃), and shading on two sides (S₄). We measured growth indices (diameter at ground level, seedling height), leaf morphological traits (leaf number, leaf area, leaf thickness, petiole length, and petiole width), chemical traits (leaf carbon (C), nitrogen (N), and phosphorus (P) contents, C∶N, C∶P, N∶P ratios, and δ¹³C), and photosynthetic traits (SPAD value, maximum photochemical efficiency of photosystem Ⅱ F_v/F_m, photosynthetic performance index, and intrinsic water use efficiency (iWUE). We further comprehensively evaluated the responses of F. danxiaensis seedlings to shading. The results showed that: (1) Shading had a greater impact on seedling height (0.67-0.97 m, P<0.05) than on diameter at ground level (8.77-10.70 mm). The growth of seedling showed an allometric growth relationship (P(α=1)<0.01). (2) Shading significantly altered petiole length and width (P<0.05) and induced significant differences in leaf C, N, and P contents, C∶N, C∶P and N∶P ratios, and δ¹³C (P<0.05). However, only the SPAD value showed significant differences among photosynthetic traits, with the value being higher in S₁ than that in CK (P<0.05). (3) Diameter at ground level displayed a significant positive correlation with seedling height (P<0.05), while leaf phosphorus concentration was positively correlated with all the measured leaf morphological traits, including leaf number, leaf area, leaf thickness, and petiole length (P<0.05). Similarly, the F_v/F_m was positively correlated with iWUE (P<0.05). Conversely, SPAD values presented significant negative correlations with leaf thickness, petiole width, and leaf C∶N (P<0.05). Leaf δ¹³C had significant negative relationships with leaf nitrogen concentration, C∶P, and N∶P (P<0.05). (4) The comprehensive quality index of shaded seedlings ranged from 0.40 to 0.48, with all shading treatments yielding higher values than the open habitat. East-side shading treatment was the most beneficial for seedling growth. Moderate retention of shaded environments in ex-situ conservation practices for F. danxiaensis can effectively enhance seedling growth, leaf photosynthetic capacity, and seedling quality.

Key words: Firmiana danxiaensis, shading, seedling growth, leaf functional trait, seedling quality index