Figure 3

The photosynthetic rate (P_n, μmol m⁻² s⁻¹), intercellular CO₂ concentration (C_i, μmol mol⁻²), transpiration rate (T_r, mmol m⁻² s⁻¹) and stomatal conductance (G_s, mol m⁻² s⁻¹) under the control treatment (CK), low drought stress (LS), moderate drought stress (MS) and severe drought stress (SS) in 2018 and 2019. (a, c, e and g) represent the values in 2018, while (b, d, f and h) represent the values in 2019. Different letters above the columns indicate significant differences (P < 0.05) determined by a Duncan’s test between treatments. The same letters above the error bars indicate no significant different at P > 0.05.