Measurement of Age and Growth Rate in the Crustose Saxicolous Lichen Caloplaca Trachyphylla Using ¹⁴C Accelerator Mass Spectrometry

Abstract

Sections of the crustose saxicolous lichen, Caloplaca trachyphylla, were dated using 14C accelerator mass spectrometry (AMS). The data show a stron linear dependence of radial position on time (r=0.993), suggesting a constant radial growth rate. This specimen had averaged a marginal growth rate of 1.48 mm/year. Extrapolation of the growth curve yields a thallus age of 20 years. These data demonstrate the feasibility of using AMS technology to precisely date lichen tissues and determine growth rates of lichen thalli.

Differences in texture, physical properties and microbiology of weathering crust and host rock: a case study of the porous limestone of Budapest (Hungary)

“…When exposed to air after flaking, the biofihn became desiccated and lost the typical blue-green colour. Similar biofilms have been frequently observed in natural habitats (see, for example , Bell 1993b;Clark et al 2000;Friedmann 2000) and on building stone (for review see Warscheid & Braams 2000). In a thin layer 1-5 mm beneath the surface, the organisms are protected from environmental stress and are exposed to optimum or at least sufficient light intensity for photoautotrophic growth.…”

“…bird droppings), the nitrophilic lichens Caloplaca or Candelariella could be detected. All lichen thalli were 0.7 mm in diameter or smaller, indicating that the thalli were not older than approximately 5 years (see Clark et al 2000).…”

The biology behind lichenometric dating curves

“…Lichenometrists call the steep portion of such curves the period of ''great growth'' (Beschel 1973;Bull and Brandon 1998;Karle´n and Black 2002), implicitly asserting that these calibration curves reflect highest radial growth rates in the smallest lichens. Lichen biologists, however, argue on both theoretical (Childress and Keller 1980) and experimental (Armstrong 1976;Proctor 1977;Hill 1981;Clark et al 2000) grounds that growth rates of individual lichens should be lowest in small thalli, increasing asymptotically towards a more or less constant rate as the curvature of the thallus rim diminishes. That the debate persists illustrates our generally poor understanding of the biological processes that govern lichen population dynamics, that give rise to lichenometric data, and that are necessary to understand before we can quantify errors associated with the technique.…”

Lichen Growth and Lichenometry

“…Zahlbr. was studied using C-14 accelerator mass spectrometry (AMS) (Clark et al 2000). Sections of lichen were dated and exhibited a linear correlation with radial location, estimated ages also suggesting that RaGR was constant over long periods of time.…”

“…A number of authors have speculated whether RC dating could be used to age lichen thalli Three phases of growth were identified as follows: (1) an early growth phase in which RaGR increased to a maximum, (2) a short phase in thalli 30-40 mm in diameter at which RaGR was maximal and (3) a phase in which RaGR declined in thalli greater than approximately 50 mm in diameter directly (Maguas and Brugnoli 1996;Clark et al 2000;Bench et al 2001). As a thallus grows radially, new tissue is produced at the margin which should be younger than the tissue in the centre.…”