Introduction
Drylands represent the largest terrestrial biome, accounting for at least 35% of Earth’s land mass (Middleton and Thomas, 1992; Peel et al., 2007). These ecosystems experience extreme daily and seasonal fluctuations in light, temperature, and water availability, often concomitantly. Interaction between extreme environmental conditions such as low water availability and high light represents a particular challenge for plants. To survive dry periods, many dryland bryophytes and a smaller number of vascular plants have evolved vegetative desiccation tolerance, defined as the ability to equilibrate to dry air and resume metabolic activity after rehydration (Gaff, 1977; Proctor et al., 2007; Stark, 2017). Yet, while desiccation tolerance allows these plants to survive dry periods by limiting metabolic activity to periods of adequate moisture availability, this adaptation implicates long periods of exposure to high light intensity during full sun, including unusable photosynthetically active radiation (PAR) and direct UV radiation, both of which may be harmful.