Abstract: Leaf economic, hydraulic and anatomical traits play crucial roles in plant adaptation to diverse and variable environments. However, their relationships at the intraspecific level remain unclear. In this study, we investigated Quercus variabilis, a species spanning temperate to subtropical zones, to assess functional trait variation along a north-to-south environmental gradient in China (24°94′–40°26′ N). We analyzed 10 key functional traits, including leaf mass per area (LMA), leaf thickness (LT), leaf tissue density (LTD), leaf nitrogen concentration (LN), stomatal density (SD), vein density (VD), stomatal guard cell length (SL), palisade tissue thickness (PT), spongy tissue thickness (ST) and palisade-to-spongy tissue ratio (PT/ST) across 9 natural populations. The results showed that Q. variabilis exhibited significant plasticity in functional trait variation, primarily driven by environmental factors, with mean annual precipitation (MAP) and soil total nitrogen (STN) emerging as key ecological drivers promoting the coordinated variation in leaf functional traits. Coordinated relationships were observed between leaf economic traits (LMA, LT, LTD, LN) and hydraulic traits (SD, VD, SL), which varied in response to environmental conditions. Furthermore, leaf anatomical traits (PT, ST, PT/ST) were closely linked to both hydraulic and economic traits. These findings provide valuable insights into the adaptive strategies of Q. variabilis and enhance our understanding of plant responses to environmental change at the intraspecific level.

Key words: functional traits, leaf economics, leaf hydraulics, leaf anatomy, intraspecific trait variation, trait coordination, environmental gradients