bright green when grown in dim, artificial laboratory light (personal observation), suggesting a plastic pigment-accumulation reaction in response to light exposure. Accumulation of dark pigmentation varies in nature, too. S. caninervis plants are greener in very low-light microhabitats (Ekwealor and Fisher, 2020) and when UV is filtered out of natural sunlight (unpublished data). This apparent “suntan” pattern suggests the possibility of an adaptive response for UV protection, though that function has not yet been tested in S. caninervis.
To this end, we conducted an integrated, four-part experiment to test how desert mosses withstand solar radiation while quiescent under natural and extreme fluctuations in climate and solar radiation characteristic of the Mojave Desert. We deployed a year-long, controlled UV-reduction manipulation on twenty in-situ microsites of S. caninervis to test the hypotheses that: (1) natural S. caninervis plants undergo sustained NPQ while desiccated and after rehydration, (2) if UV radiation is a stressor then a reduction of natural levels of UV will result in improved recovery of maximum PSII quantum efficiency (Fv/Fm) but (3) one year of UV removal will de- harden plants and thus increase vulnerability to UV damage, indicated by a reduction in Fv/Fm after an laboratory UV treatment. In order to better understand the mechanisms of photoprotection, UV tolerance, and recovery from desiccation, we measured relative abundance of photosynthetic pigments and antioxidants in field-manipulated plants, and quantified differential transcript abundance on UV-reduced plants and controls. Finally, to understand the effects of the high light and desiccating natural environment on the pigment and antioxidant profiles, we compared field-collected, un-manipulated S. caninervis plants to those cultured in a laboratory growth chamber.