Intrathalline and size‐dependent patterns of activity in Lasallia pustulata and their possible consequences for competitive interactions

Abstract

Summary 1.In dense populations of the saxicolous lichen Lasallia pustulata the margins of adjacent thalli overlap each other in intraspecific competition for space and light. 2. In situ non-destructive monitoring of hydration-dependent potential photosynthetic activity by modulated fluorescence systems in different parts of the thallus shows that the activity is structured by a centre-to-margin gradient, with the centre of the thallus remaining active for substantially longer periods than the margins when the thalli dry up after being activated by wetting. The pattern reflects the water status of different parts of the thallus; the margins which are thin and exposed dry up first. 3. The activity pattern within individual lichen thalli suggests that marginal overlapping between neighbours may have a less detrimental effect on the shadowed individuals than expected from a pure consideration of the amount of area shadowed. Because the centre of the lichen thallus is active for longer periods, shadowing of this region may possibly be more harmful per area unit than an overlap at the less active margins. 4. Larger thalli are active for substantially longer periods than small ones. Even the margins of larger thalli tend to be active for a longer period than the centre of small thalli. Key-words:Competition, intrathalline activity, lichens, overlap, size-dependent performance Functional Ecology (1997) 11, [318][319][320][321][322] 319 Intrathalline patterns of activity in L. pustulata strictly dependent on thallus water content which fluctuates strongly with the external conditions (Kappen 1988;Rundel 1988). Carbon gain and growth is limited to brief periods of favourable moisture conditions. Thus water must be judged the primary limiting resource.With modulated fluorescence systems it is now possible to monitor hydration-dependent potential photosynthetic activity of lichen thalli non-destructively in situ (Schroeter, Kappen & Moldaenke 1991;Schroeter et al. 1992;Schroeter 1994). In the present study we apply this new technology to characterize intrathalline and size-dependent patterns of activity in L. pustulata as a first step towards an understanding of competitive interactions in populations of this lichen. Materials and methodsLasallia pustulata grows in abundant populations on sun-exposed, more or less vertically inclined, often south-facing cliffs and outcrops of siliceous rocks along the coast of southern Norway. Attached to the substrate by only a central holdfast, the peltate thallus is elevated slightly above the rock surface when dry. Individual thalli may reach sizes of up to 35 cm in diameter (Hestmark, unpublished observation), although they are usually much less. Populations include individuals of many sizes (Hestmark 1992).The field measurements were conducted in the Hvaler archipelago (59°N, 10°E), Østfold, southern Norway, in May 1994. The bedrock in the area is dominated by granite providing suitable habitat outcrops for large populations of L. pustulata and other umbilicate lichens such as Umbilic...

The significance of thallus size for the water economy of the cyanobacterial old-forest lichen Degelia plumbea

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“…Very few studies have focused on size-dependent physiological processes in lichens (Larson 1979(Larson , 1984Hestmark et al 1997). Small thalli have a low boundary layer resistance which may cause a high water loss rate (Homan and Gates 1970;Green et al 1985); small thalli may also have a low water-holding capacity (Degelius 1935).…”

Content of secondary compounds depends on thallus size in the foliose lichen Lobaria pulmonaria

“…Stephenson & Rundel 1979;Golojuch & Lawrey 1988;Hesbacher et al 1996;Nybakken et al 2004;Gauslaa & McEvoy 2005). Furthermore, few physiological and ecological studies of lichens focus on the importance of thallus size (Golojuch & Lawrey 1988;Hestmark et al 1997;Gauslaa & Solhaug 1998), despite the probable importance of thallus size effects in lichen ecophysiology (Larson 1984). Golojuch & Lawrey (1988) showed that in Vulpicida pinastri, the concentration of the coloured vulpinic and pinastric acids increases with thallus size, but is not correlated with habitat factors.…”

The influence of environmental factors on the spatial distribution of saxicolous lichens in a Norwegian coastal community

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