| Abstract: | The combined effects of desiccation and irradiance on the physiologyof the sand dune moss Tortula ruraliformis (Besch.) Grout andthe minerotrophic flush moss Dicranella palustris (Dicks.) Crundw.ex. E. F. Warb (D. squarrosa (Starke) Schp.) were studied. Damageas a result of desiccation in the dark, measured by loss ofprotein and the relative accumulation of thiobarbituric acid(TBA) reactive products (which gives an estimation of lipidperoxidation), was greater in D. palustris. Desiccation alonehad no effect on the total concentrations of chlorophyll andcarotenoids in either species. Water loss resulted in the cessationof measurable photosynthetic oxygen evolution in both species.Respiration was less sensitive to desiccation than was photosynthesis.A combination of irradiance and water stress prevented any recoveryof photosynthesis during subsequent rehydration in D. palustris,but suppressed recovery only marginally (at the highest irradiance)in T. ruraliformis. The loss of protein, chlorophyll, and carotenoids,and lipid peroxidation were all substantially increased in D.palustris desiccated in the light, but these same conditionsresulted in only minimal damage of T. ruraliformis. Continuousexposure to high irradiance was less deleterious to desiccatedthan hydrated T. ruraliformis. The data are discussed in relationto the habitat preferences of the two species, and also in relationto possible causal factors in the initiation of damage. Key words: Desiccation, mosses, oxidative damage, photo-oxidation |
