Salinity responses of halophytic and non-halophytic bryophytes determined by chlorophyll fluorometry

Abstract

The mosses Schistidium maritimum and Tortella flavovirens are halophytes growing in the supralittoral zone of rocky shores, where they are exposed to wave splash, occasional tidal immersion and desiccation. We investigated their recovery from desiccation and their metabolic activity when moistened by seawater and distilled water, taking the non-halophytes Atrichum undulatum and Eurhynchium striatum for comparison, and using chlorophyll fluorescence to monitor photosynthetic efficiency. All the species, regained photosynthetic capacity after rewetting with seawater, although the maximum quantum efficiency (Fv/Fm) attained in seawater was lower than in distilled water. Switching the treatments indicated that the depression of Fv/Fm was probably an osmotic effect. Under ambient laboratory lighting 17 days' seawater treatment had little effect on S. maritimum but brought about some decline of Fv/Fm in A. undulatum. At ca 350 μmol m–2 s–1 PPFD, 10 days' seawater treatment caused a rapid and severe decline of Fv/Fm in A. undulatum, and a lesser decline in S. maritimum. Isotonic PEG 6000 caused a reduction in Fv/Fm comparable to that in seawater. This suggests that osmotic stress increases susceptibility to photo-injury. In all species RETR was lower in seawater; 1-qP increased in seawater in all the species but only slightly in S. maritimum. NPQ was lower in seawater than in distilled water in the non-halophytes A. undulatum and E. striatum, but higher in seawater in the halophytes, in which it increased steeply with irradiance, suggesting a higher capacity for harmless dissipation of excess excitation energy in the halophytes.