The lichen cushion: A functional perspective of color and size of a dominant growth form on glacier forelands.

Mat-forming lichens dominating high-latitudinal habitats vary in color and geometry. Widespread species are light greenish yellow (usnic acid) and reflect solar radiation, whereas melanic species absorbing most solar wavelengths are spatially more restricted. Color thereby influences lichens' energy budget and thus their hydration and photosynthetically active periods.

Functional trade-off of hydration strategies in old forest epiphytic cephalolichens.

Although water is essential for photosynthetic activation in lichens, rates of vapor uptake and activation in humid air, which likely influence their niche preferences and distribution ranges, are insufficiently known. This study simultaneously quantifies rehydration kinetics and PSII reactivation in sympatric, yet morphologically and functionally distinct cephalolichens (Lobaria amplissima, Lobaria pulmonaria, Lobaria virens). High-temporal resolution monitoring of rehydrating thalli by automatic weighing combined with chlorophyll fluorescence imaging of maximal PSII efficiency (F/F) was applied to determine species-specific rates of vapor uptake and photosynthetic activation.

Photobiont-dependent humidity threshold for chlorolichen photosystem II activation.

Photobiont type influences the relative humidity threshold at which photosystem II activates in green algal lichens. Water vapor uptake alone can activate photosynthesis in lichens with green algal photobionts. However, the minimum relative humidity needed for activation is insufficiently known.

Why chartreuse? The pigment vulpinic acid screens blue light in the lichen Letharia vulpina.

Chlorophyll fluorescence, infrared gas exchange and photoinhibition data consistently show that vulpinic acid in L. vulpina functions as a strong blue light screening compound. The cortical lichen compounds, parietin, atranorin, usnic acid and melanins are known to screen photosynthetically active radiation (PAR), thereby protecting the underlying photobionts.