Fig. 7.

The response of chlorophyll fluorescence parameters (see Table 1 for full descriptions) in the wheat cultivar T. aestivum ‘Pavon76’ to stepwise increases in Photosynthetic Photon Flux Density (PPFD) from 0 to 100% (0–1027 umol m⁻² s⁻¹ PPFD) under 20 (white circle) or 200 (black circle) mmol mol⁻¹ O₂. After a dark adaptation period of 1 h, maximum PSII efficiency was determined (a—F_v/F_m). From the dark-adapted values of maximal (F_m) and minimal (F_o) fluorescence, the following parameters can be calculated: operating efficiency in the light (b—F_v′/F_m′), PSII quantum yield of PSII (c—F_q′/F_m′), fraction of open PSII reaction centres (d—qP) and non-photochemical quenching (e—NPQ) and. Data are the mean ± SE (n = 4). Asterisks indicate significant differences where ‘***’P < 0.001 ‘**’P < 0.01 ‘*’P < 0.05