Plant materials
The deciduous oriental oak (Q. variabilis ) is one of the most widely distributed trees across Eastern Asia (Chen et al. 2012), which provides ideal experimental samples to explore the spatial variation and driving factors of functional plant traits under climate change. In the present study, the sampled sites spanned latitudes from 24°N to 51.8°N, and longitudes from 99°E to 137°E (Fig. 1). The mean annual temperatures (MAT) ranged from 8.7 to 22.8°C, mean annual precipitation (MAP) from 495 to 2600 mm, and mean monthly solar radiation (MMSR) from 298.2 to 541.6 (MJ m-2) (Du et al. 2021). In previous studies, spatial variations in leaf vein density (Zhu et al. 2012) and stomatal traits (Du et al. 2021) have been examined in oriental oak.