Plant species that lives in coastal dune environments are exposed to a wide range of light intensities, depending on their growth site, the time of the day and the season. In response to such changing light conditions plants may display a variety of morphologies, leaf structures and life forms, but also in the shape of their photosynthetic light response curves. These differences may reveal characteristics of the underlying photosynthesis processes including the light-dependent and light-independent reactions, the efficiency at which light is utilized by photosynthesis, and even the rate of CO2 uptake.
In this study, we tested, under field conditions, for variation in light responses curves in four co-occurring dune species. Light response curves were obtained by measuring the effective quantum yield of Photosystem II at increasing levels of photosynthetic activeradiation (PAR). Before determination of quantum yields, leaves of each species were illuminated during 3 minutes at the predetermined levels of radiation (0, 50, 100,200, 350, 600, 1000 and 1500 µmol•m-2•s-1 of PAR). Following that, the light was switched off and recovery curves were determined, at 1, 5 and 20 minutes after dark adaptation. Measurements were made on February and repeated on July 2008. Using repeated measures analysis of variance, we found significant among species variation in light and recovery curves.
Results/Conclusions
Matthiola sinuata showed the highest values of photochemical efficiencies at the predetermined levels of radiation, whereas Pancratium maritimum showed the lowest values. For recovery curves, M. sinuata showed significant differences with P. maritimum and Eryngium maritimum, but no differences were found among the other species. Differences among species in light response curves and recovery curves are expected to increase as the season progress.
