Elevational variation in leaf anatomical and stomatal traits and their allometric relationships of Quercus variabilis from a warm-temperate forest.

Leaf anatomical structure and stomata play pivotal roles in optimizing and regulating photosynthesis and transpiration. Exploring the plastic variability and allometric relationships of leaf anatomical and stomatal traits across an elevational gradient is of great significance for revealing plants' adaptation strategies to varying environments. This study focused on Quercus variabilis distributed at elevations of 800-1500 m on Mt. Li, a warm-temperate forest zone in China. We assessed the elevational variation in leaf anatomical and stomatal traits, and determined the allometric relationships among these traits using standardized major axis regression. With increasing elevation, the five anatomical traits overall exhibited a synergistic increasing trend, including leaf thickness (LT), palisade tissue thickness (PTT), spongy tissue thickness (STT), upper epidermis thickness (UET), and lower epidermis thickness (LET). Stomatal length (SL), width (SW), and area (SA) presented trend first increasing then decreasing, while stomatal density (SD) and stomatal area fraction (SAF) demonstrated the opposite pattern. SAF was primarily determined by SD rather than SA, despite a stable negative correlation between SD and SA. Additionally, five anatomical traits were significantly positively correlated with SD and negatively correlated with SA. Importantly, PTT, STT, LT, and SD, exhibiting higher plastic variability, had allometric relationships with other traits and demonstrated a faster rate of change. Our findings suggest that Q. variabilis leaves tend to be thicker, with smaller and denser stomata at higher elevations. The plastic adjustments of palisade tissue, spongy tissue, and stomatal density are crucial for Q. variabilis to adapt to heterogeneous habitats caused by elevational gradients.