Fig. 4 Effects of drought preconditioning on canopy photosynthetic rate (P_n) (A) and photochemical efficiency (Fv/Fm) (B) of Kentucky bluegrass under subsequent heat stress. Pre+H, drought preconditioning under subsequent heat stress; Non+H, non-preconditioning under heat stress; Pre+D+H, drought preconditioning under the combination of drought and heat stresses; Non+H+D, non-preconditioning under the combination of drought and heat stresses. Vertical bars indicate LSD values for treatment comparisons at a given day of treatment