Photosynthetic Responses to Light Intensity of Sarcocornia Taxa (Chenopodiaceae)

Salt marshes show a characteristic zonation of species distribution, which is correlated with marsh elevation. Radiation intensity and photoperiod change throughout the tidal frame. Photosynthetic response to light regime, 90-2450 mu mol/(m(2) s), was determined in the laboratory for four closely related halophytic taxa of the genus Sarcocornia (Chenopodiaceae), which inhabit different positions in the tidal frame. Sarcocornia fruticosa, which germinates below vegetation cover and is found at high levels in the tidal frame, had the lowest maximum net photosynthetic rate and stomata conductance values. The two S. perennis subspecies demonstrated intermediate maximum net photosynthetic rates but S. perennis ssp. alpini reached light saturation point at higher light intensities. S. perennis ssp. perennis, found in the lowest elevations of the marshes, spends a significant proportion of its time submerged and therefore needs to take full advantage of available light. S. perennis ssp. alpini is exposed to very high light intensities in open salt pans at high elevations. The hybrid, S. perennis x fruticosa, which is currently found at intermediate elevations with less frequent inundation, had the highest net photosynthetic rate and chlorophyll a content. The ability to cope with high light levels may help to explain one of the environmental parameters, which affects distribution of four taxa throughout the tidal frame and also raise intriguing questions about the future role of the hybrid in the successive development of these marsh systems.