stomatal conductance (Cond) of the same leaves were measured with a Portable Photosynthesis System (Li-Cor 6400, Li-Cor Inc., USA), and the photosynthetic measurements were conducted at 1200 μmol m− 2 s− 1 radiation intensity on clear mornings (at 09:00–11:00, 3–4 h after sunrise). The mean of three measurements was used to represent the corresponding parameter for each plot.