Fluorescence remote sensing detection of freshwater and saltwater flooding in the evergreen shrub, Myrica cerifera

Photosynthesis, water relations, and chlorophyll fluorescence were used to evaluate stress due to freshwater and saltwater flooding in the evergreen coastal shrub, Myrica cerifera.  Myrica cerifera forms large monospecific thickets that enable scaling up from leaf-level measurements to the landscape.  Based on physiological responses, stress began by day 3 in flooded plants treated with 5, 10, and 15 ppt salinity, as seen by significant decreases in stomatal conductance and photosynthesis relative to control plants.  Decreases in physiological measurements occurred by day 9 in freshwater flooded plants.  Visible signs of stress occurred by day 5 for plants treated with 15 ppt, day 6 for flooded plants exposed to 10 ppt, and day 9 for those treated with 5 ppt salinity.  In comparison, significant differences in light-adapted fluorescence (Fv′/Fm′) were observed by day 3 in flooded plants treated with 5, 10, and 15 ppt salinity.  Statistical differences in the traditional dark-adapted fluorescence parameter, Fv/Fm, were observed in plants flooded with 5, 10, and 15 ppt salinity by day 12 of the experiment, well after visible signs of stress were apparent.  Corresponding reflectance data indicated stress by day 9 in the higher salinity flooded plants.  Our results show light-adapted fluorescence measurements were more sensitive than dark-adapted fluorescence measurements as indicators of stress.  Light-adapted fluorescence appears to be more useful in detecting stress induced changes in the photosystem before any visible signs of damage are evident, and may be linked to hyperspectral reflectance data for rapid detection of stress at the canopy level.