Species‐specific activation time‐lags can explain habitat restrictions in hydrophilic lichens

Abstract

Photosystem II (PSII) activation after hydration with water or humid air was measured in four hydrophilic and a generalist lichen to test the hypothesis that slow activation might explain habitat restriction in the former group. For the hydrophilic species, activation was after 4 h nearly completed in Lobaria amplissima and Platismatia norvegica, while only c. 50% for Bryoria bicolor and Usnea longissima. The generalist Platismatia glauca was activated instantaneously. The effect of this on lichen field performance was investigated using a dynamic model separating the two water sources rain and humid air. Model simulations were made using the species-specific characteristics and climate data from 12 stream microhabitats. For U. longissima, slow PSII activation could reduce realized photosynthesis by a factor of five. Bryoria bicolor was almost as severely affected, while P. norvegica displayed moderate reductions. Lobaria amplissima displayed longer realized activity periods even in unfavourable microclimates, possibly because of a higher water loss resistance. Both close proximity to streams and presence of turbulent water had a positive impact on realized activity among the slowly activated species, coinciding with observed distribution patterns of hydrophilic species. The results presented here may thus partly explain observed habitat restrictions of rare hydrophilic lichens.

Rain, dew, and humid air as drivers of morphology, function and spatial distribution in epiphytic lichens

“…In marked contrast, direct exposure to sunlight causes rapid drying (Lange et al 2004) and adversely impacts epiphytic lichen growth (Gauslaa & Goward 2012;Bidussi et al 2013b), although short-time sunflecks can have positive effects (Lakatos et al 2006;Coxson & Stevenson 2007a). Light experienced during prolonged dry periods causes much more damage than desiccation per se, and substantially retards photosynthetic activation during subsequent hydration , particularly in epiphytic cephalolichens and shade-adapted chlorolichens (Gauslaa & Solhaug 1996;Jonsson Cabrajic et al 2010).…”

Estimating global carbon uptake by lichens and bryophytes with a process-based model

“…A further property of the relation between water content and metabolic activity is that in some species, the metabolic activity corresponding to a certain water content is only reached after a time delay (Jonsson et al, 2008;JonssonČabrajić et al, 2010;Lidén et al, 2010). The delay is not only species-specific, but it also depends on the length of the preceding dry period (Ried, 1960;Gray et al, 2007;Proctor, 2010).…”

“…If the water saturation is above this threshold, all cells in the thallus are fully turgid and extracellular water may exist inside the thallus or on its surface; and 3. The metabolic activity of a lichen or bryophyte, which determines both the relative strength of photosynthesis as well as that of respiration as a function of water saturation (Lange, 1980(Lange, , 2002Lidén et al, 2010;Williams and Flanagan, 1998). The metabolic activity is assumed to increase linearly from 0 at zero water saturation to 1 at the threshold saturation.…”

Photosynthetic traits of freshwater lichens are consistent with the submersion conditions of their habitat

“…These differences are consistent with the duration of submersion undergone by the lichen in its natural environment and may partly explain habitat distribution patterns of the sub-versus the hyper-hydrophilic species. The present differences between sub-and hyper-hydrophilic freshwater lichens were smaller than those of species-specific patterns of PSII activation timelags and water-holding capacity which allowed Liden et al (2010) to explain habitat restriction. However, following Jonsson-Cabrajic et al (2010), we consider that slightly slower activation (6 min against 1 min) and higher sensitivity of PSII to desiccation may be important factors to explain the confinement of the most freshwater-related species to habitats that provide sufficiently long hydration periods.…”

“…Exposure to (strong) light in the desiccated state has been shown to cause reduction in quantum efficiency (Gauslaa and Solhaug, 1996). In previous studies, it has often been assumed that wet and illuminated lichens are fully photosynthetically active and that photosynthetic activation in lichens occurs instantaneously (Coxson, 1988;Lange et al, 1989;Palmqvist and Sundberg, 2000;Dahlman and Palmqvist, 2003;Liden et al, 2010). However, a few publications report a lag time of several hours with suboptimal photosynthetic activity following liquid hydration of dry thalli (Lange et al, 1986).…”