Effects of high light intensity and desiccation stress on moss species.

Abstract

Bryophytes are desiccant tolerant non-vascular plants, capable of growing and surviving in extreme conditions. They are divided into three groups: liverworts, hornworts, and mosses. Most mosses grow in shady and moist environments, although some formpart of arid soil crusts where they protect soil from erosion. The moss flora of the Afromontane vegetation around Pietermaritzburg is dominated by two acrocarpous mosses, Atrichum androgynum, and Dicranella subsubulata. A. androgynum tends to grow in wetter, more shaded habitats and is a rather delicate species, while D. subsubulata grow in open, drier habitats and is more robust. Rarely, the species grow together, for example at the transition of a shaded indigenous woodland to plantations. We hypothesized that the more robust species has higher stress tolerance and has largely constitutive stress tolerance mechanisms. By contrast, we hypothesized that the more delicate species is less tolerant and may have inducible tolerance mechanisms. In the present study, desiccation tolerance and tolerance to high light stress were investigated in A. androgynum and D. subsubulata. Results confirmed that D. subsubulata was more tolerant of high light stress than A. androgynum. Exposure to moderate light intensities did not increase tolerance to subsequent high light stress in either species. Similarly, D. subsubulata was more desiccation tolerant than A. androgynum. Not consistent with our original hypothesis, mild desiccation, and treatment ABA-induced tolerance to desiccation in both species. Furthermore, detailed studies of the antioxidant enzyme peroxidase showed that enzyme activity was induced during slow drying in both D. subsubulata than A. androgynum. It appears that inducible tolerance mechanisms are present in both species. The work presented here represents a contribution to the autecology of two important mosses in the KwaZulu-Natal midlands Afromontane vegetation.