Mean (a) photosynthetic rate (A_max), (b) stomatal conductance (g_s), and (c) water-use efficiency (WUE_i) for control, artificial and insect defoliation treatments on four occasions (D0, D5, D17, D23). Error bars show least square differences (α < 0.05). LSD homogeneous groupings are identified by letters (α < 0.05).