Photosynthesis and Water Relations of Lichen Soil Crusts: Field Measurements in the Coastal Fog Zone of the Namib Desert

Although the coastal fog zone of the Namib Desert has negligible rainfall, large parts may be covered by soil-crust lichens with chlorophyll contents and photosynthetic rates (under optimal conditions of hydration and light), on an area basis, almost equal to the leaves of typical higher plants. The photosynthetic and respiratory CO 2 exchange rates of three soil-crust lichens, Acarospora cf. schleicheri, Caloplaca volkii and Lecidella crystallina were measured in the field (September 1990). The three species responded in a similar fashion to changing environmental conditions. Nocturnal hydration, by fog and/or dew, activated dark respiration which was followed after sunrise by a short period of positive net photosynthesis that continued until metabolic inactivation occurred from desiccation (...)