Spatial variations in leaf trichomes and their coordination with stomata in Quercus variabilis across Eastern Asia

Understanding leaf trait variation is critical for the prediction of plant responses to global climate changes. Leaf trichomes are derived from stomatal epidermal cells, which play critical roles in biotic defenses and against abiotic stress. Previous studies reported spatial variations in stomatal traits and their driving factors at the same sampling sites. However, it remains unclear how leaf trichome densities vary along large geographic gradients and whether trichomes and stomata co-vary under environmental changes. We measured the leaf trichome densities of 44 Quercus variabilis populations in situ across Eastern Asia (24 to 51.8 °N, 99 to 137 °E) and 15 populations grown in a common garden, and used structural equation modelling to evaluate their relationships with climatic factors and stomatal traits. Our results revealed that climatic factors not only had a direct effect on trichome density, but also had indirect effects on trichome density through stomatal density and leaf mass per area. Trichome density was positively correlated with stomatal density whether in situ or in the common garden, and both increased with drought, which implied that trichomes may impact stomatal behavior and both traits may co-vary under certain environmental conditions. Our results suggested that leaf trichomes possess highly adaptive variation and are in close coordination with stomata in response to climate changes. Our findings provide new insights toward elucidating the interactions between leaf traits and the adaptive strategies of plants under climate change.