Trichome and leaf functional trait measurements
The measurement of trichome density in oriental oak was similar to stomatal measurement that reported in previous study (Du et al. 2021). Firstly, the trichomes at the right side of the midrib in the central section of the lower leaf surface were gently removed with a blade under an anatomical lens, and then one 0.5 × 0.5 cm2 section was selected as a sample. Subsequently, the samples were fixed in 2.5% glutaraldehyde and stored in a refrigerator at 4ºC. Prior to being imaged, the samples were in turn dehydrated using an ethanol gradient, freeze-dried, and gold sputtered, after which three graphs for each sample were collected at 1000× magnification with a FEI Sirion 200 ultrahigh resolution Schottky field emission scanning electron microscope (FEI Company, Hillsboro, OR, USA). The trichome density was calculated by averaging 45 images per population with a 0.056 mm2 viewing field.
The methods of measurement of the SD and SS were described in Du et al. (2021). The LA was determined with WinFolia software (Regent Instrument Inc. Quebec, Canada), whereas the leaf dry mass was measured after drying at 70ºC for 48h. The LMA was obtained as the dry mass per unit leaf area. Leaf veins were measured with a Leica DM 2500 microscope (Leica Microsystems, Wetzlar, Germany), and VD were defined as the lengths of leaf veins per area, which were measured with Image J software (Zhu et al. 2012).