Fig. 3.

Representative fluorescence parameters measured by FRRF during consecutive increasing photon flux treatments (dark–light transient and following increases in photon flux, indicated by upward arrows) and darkness (downward arrow). a F′, F _m′ on the primary ordinate, and NPQ on the secondary Y-axis; b σ_PSII (Sigma PSII) and maximal quantum yields as well as effective quantum yield during the irradiance treatment. Photon fluxes were 50, 200, 340 and 470 μmol photons m⁻² s⁻¹. Results were confirmed in two independent experiments