Linking Leaf Chlorophyll Fluorescence Properties to Physiological Responses for Stress Detection in Coastal Plant Species

摘要

Effects of salinity and drought on physiology and chlorophyll fluorescence were used to evaluate stress in two coastal plants, Myrica cerifera (L.) and Phragmites australis (Cav.) Trin. ex Steud. Drought and salinity stress were induced and measurements of stomatal conductance, photosynthesis, xylem pressure potential (c) and fluorescence were conducted following treatment. The onset of stress began at 2 g l21 for M. cerifera, and 5 g l21 for P. australis, as seen by significant decreases in physiological measurements. Despite the physiological effects of salinity, there was no significant difference in darkadapted fluorescence (Fv/Fm, where Fm is the maximal fluorescence in darkadapted leaves) for either species at any salinity level. Significant decreases in the light-adapted measurement DF/Fm (Fm is maximal fluorescence in lightadapted leaves) occurred at 10 g l21 in M. cerifera and P. australis, days before visible stress was evident. The quantum yield of xanthophyll-regulated thermal energy dissipation (FNPQ, where NPQ is non-photochemical quenching of chlorophyll fluorescence) increased with decreasing DF/Fm. Drought studies showed similar results, with significant decreases in physiological measurements occurring by day 2 in M. cerifera and day 4 in P. australis. Differences in DF/Fm were seen by day 5 for both species, whereas Fv/Fm showed no indication of stress, despite apparent visible signs. Xanthophyll-cycle-dependent energy dissipation may be the underlying mechanism in protecting photosystem II from excess energy in salinity- and droughttreated plants.