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 (F v /F m ) attained in seawater was lower than in distilled water. Switching the treatments indicated that the depression of F v /F m 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 F v /F m in A. undulatum. At ca 350 mmol m 22 s 21 PPFD, 10 days' seawater treatment caused a rapid and severe decline of F v /F m in A. undulatum, and a lesser decline in S. maritimum. Isotonic PEG 6000 caused a reduction in F v /F m 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.

Effects of salinity stress on cellular location of elements and photosynthesis in Ramalina canariensis Steiner

“…However, under the low light conditions used in this study, photo-injury is unlikely to occur. Therefore, F v /F m can be used as a direct indicator of saline stress, as shown in previous studies (Branquinho et al 1997a, b;Bates et al 2009). …”

Sphagnum abundance and photosynthetic capacity show rapid short-term recovery following managed burning

“…Recovery of structural and photosynthetic tissues could thus occur at different rates and stages; further work on physiological responses to fire in Sphagnum may clarify mechanisms and rates of recovery. Other disturbances such as desiccation, nitrate deposition and salinity have been found to lead to F v /F m decreases of similar magnitude in Sphagnum species (0.75-0.85 to 0.05-0.5;Hájek and Beckett 2008;Bates et al 2009;Manninen et al 2011).…”

“…Approximately 2 years following fire, S. capillifolium F v / F m in burnt plots was lower than in unburnt but within the range of healthy plants, considered to be around 0.75 (range: 0.55-0.85) in bryophytes (Van Gaalen et al 2007;Hájek and Beckett 2008;Bates et al 2009;Manninen et al 2011;Taylor et al 2017) and so differences in physiological functioning were likely negligible. Given the relatively rapid recovery of S. capillifolium F v /F m following fire-induced heating, at least during the first 100 days (Taylor et al 2017), and its resilience to other disturbances such as drought (Hájek and Vicherová 2014) and high exposure to light (Maraschall and Proctor 2004), we hypothesise that sustained differences between burnt and unburnt plants are a result of microclimatic changes brought about by fire.…”

Schistidium maritimum(Sm. ex R. Scott) Bruch & Schimp. subsp.piliferum(I.Hagen) B. Bremer in Shetland, new to the British Isles

“…It is one of our few truly halophytic mosses (Richards, 1932;Bates, Wibbelmann & Proctor, 2009) and is almost entirely confined to maritime rocks just above the high water mark, where it is often the only bryophyte present. It is easily recognized in the field by its dense, dark green cushions, the narrow and rather rigid leaves without hair-points, the immersed capsules and the characteristic maritime habitat.…”