The actual photochemical efficiency of PSII in the saturated light (Fv′/Fm′),
quenching of photochemical efficiency of PSII (qP), and the quantum yield of non-cyclic
electron transport (PhiPSII) and apparent quantum efficiency (PhiCO2) of winter wheat
in the measurement at the mid-grain filling stage under ambient [O3] (A-O3) and
elevated [O3] (E-O3) (mean ± SD, n = 3). The letters on top of the bars are based on the
Tukey test across the four measurements. Bars without a same letter are significantly
different from each other at P b 0.05.