Print PageMicrobiotic soil crusts contain a diverse community of fungi, bacteria, lichens, and free-living green algae. The green algal crust residents originate from a broad diversity of taxa, representing numerous independent evolutionary transitions to a terrestrial habitat. Survival in desert soils requires tolerance of desiccation, high radiation, and extreme temperatures, all of which are rare in the aquatic environments where the majority of free-living green algae live. High incoming radiation levels require adaptation of photosynthetic pathways, in order to dissipate excess energy and avoid photodamage. Using two desert algal species, each paired with a closely related aquatic species, we examined the induction of photoprotection under conditions of high light exposure.
Results/Conclusions
We used two measures of photoprotection: non-photochemical quenching (NPQ), and the cycling of xanthophyll pigments. In both desert species, and in one of the aquatic species, NPQ was not minimized in the dark, but instead declined upon exposure to low levels of light. The remaining aquatic species, Entransia fimbriata, matched the pattern observed in higher plants, in which NPQ is lowest after dark adaptation. Cycling of xanthophyll pigments paralleled changes in NPQ in Entransia and one of the desert species, but in the other two species pigment content changed little in response to light exposure. These results indicate that some of these species maintain physiological states usually associated with photoprotection, even in the dark. Further, unlike in higher plants, there is an inconsistent relationship across taxa between xanthophyll pigment conversion and NPQ development.
