Abstract:

Background & Aims: East Asia represents a crucial refugium for Tertiary relict flora. Molecular phylogeographic studies have elucidated the divergence history between its northern and southern subregions. Nevertheless, current understanding regarding the evolutionary patterns and underlying drivers of traits remains relatively limited. 

Methods: We investigated Lindera obtusiloba by integrating field surveys and common-garden experiments to examine the geographic distribution patterns and drivers of its phenotypic and physiological trait variation. We applied principal component analysis (PCA) to characterize leaf-trait distribution patterns, and used ANOVA, redundancy analysis and multiple linear regression analysis to quantify population differences and environment-trait correlations. 

Results: Leaf size and shape exhibited certain variations, with the most pronounced differences observed in the southwest region relative to other regions. In the common garden, the southeast region showed the most significant differences in leaf traits compared with other regions, and temperature, light, and soil significantly correlated with leaf traits. For seeds, the greatest differences in color, weight, and maturity time were detected between northern and southern populations, followed by differences between the southeast and southwest regions. We found no significant correlation between environmental factors and seed weight. In the common garden, germination and phenological development differed significantly among plants from different regions. Regarding other phenological characteristics, we observed more obvious differences between the northern and southeast regions. The seedling survival rate was lowest in the southwest region, while the seedling growth rate and magnitude of variation were highest in the southeast region. We detected no significant differences in the light saturation point of seedlings from the three regions; the light compensation point was the lowest in seedlings from the northern region, and the maximum net photosynthetic efficiency was the highest in seedlings from the southeast region. 

Conclusions: Accordingly, the phenotypic traits of L. obtusiloba exhibit a clear geographical distribution pattern. Environmental factors predominantly regulate leaf-related traits, whereas genetic factors primarily shape seed-related and physiological traits. This research analyzes the associations among trait evolution, genetic differentiation, and environmental variables, offering substantive empirical evidence for investigating the evolutionary trajectories of Tertiary relict plants.

Key words: field investigation, common garden experiment, leaf shape, seeds, phenology, photosynthesis