Fig. 1.

Non-photochemical quenching (NPQ) measured in leaves of Col-0 plants during 7-day exposure to different light regimes. NPQ was induced by illumination at 1,000 μmol photons m⁻² s⁻¹ (indicated by a white bar above the x-axis) for 8 min and dark relaxation was monitored subsequently for 14 min. The different light regimes in the climate chamber were: constant PAR of a ca. 50 (C 50), b 85 (C 85) and f 120 μmol photons m⁻² s⁻¹ (C 120) with a photoperiod of 12 h/12 h day/night; c long sunflecks of 650 μmol photons m⁻² s⁻¹ once a day at around midday (LSF 650); short sunflecks of d 650 μmol photons m⁻² s⁻¹ applied every 6 min (SSF 650/6), or 1,250 μmol photons m⁻² s⁻¹ every e 12 (SSF 1250/12) or g 6 min (SSF 1250/6). The treatments with LSF and SSF were performed under the C 50 condition. The daily total PAR was about a 2.1, b–e 3.6 or f and g 5.1 mol photons m⁻² day⁻¹. Plants were grown under C 50 and the light treatments were started on day 0. The maximal PSII efficiency of dark-adapted leaves (F _v/F _m) at the beginning of the measurements was 0.79~0.82 for all plants throughout the 7-day experiment. Data are means of five plants (±SE)