Photoinhibition in differently coloured juvenile leaves of Syzygium species

Photoinhibition, as measured by the dark-adapted chlorophyll a fluorescence ratio Fv/Fm, was assessed in Syzygium moorei, a species with dark green juvenile leaves, Syzygium corynanthum, which has light green juvenile leaves, and two species with pink-red juvenile leaves (Syzygium wilsonii and Syzygium luehmannin. All plants were glasshouse-grown (maximum PPFD 1500 μmol m−2s−1) under optimum nutrition and water. When measured at midday, dark-adapted Fv/Fm ratios of juvenile leaves gradually increased in all species as percentage of full leaf expansion (% FLE) increased. Fluorescence measurement 3 h after sunset or pre-dawn also showed a developmental effect on Fv/Fm, with juvenile leaves of S. luehmannii and S. wilsonii showing much lower Fv/Fm at all stages of development. Dark-adapted Fv/Fm values in both juvenile and mature leaves generally never exceeded 0.8 at any stage in any of the species. Courses of Fv/Fm on sunny days showed greater diurnal photoinhibition in green juvenile (c. 50% FLE) leaves of S. moorei (24%) and S. corynanthum (36%) than in mature leaves of the previous flush in these species (< 10%). Diurnal photoinhibition was statistically similar (18–24%) in pink-red juvenile and green mature leaves of S. luehmannii and S. wilsonii. Re-positioning juvenile leaves of S. wilsonii horizontally increased diurnal photo inhibition. Exposure of leaves to a standard mild photoinhibitory light treatment (30 min at 1000 umol m−2s−1) showed that juvenile leaves of all species had a lower percentage of high energy state quenching (qE) and a higher percentage of photoinhibitory quenching (ql) than mature leaves.