Accurate lifespan estimates cannot be obtained from ¹⁴C profiles in the crustose lichen Rhizocarpon geographicum (L.) DC.

Abstract

Radial 14C/C profiles across three individuals of the crustose lichen Rhizocarpon geographicum (L.) DC. have been determined using accelerator mass spectrometry. These data were used to assess whether lifespan estimates can be determined in this species using 14C/C isotope ratio measurements. 14C/C profiles are relatively flat with Δ14C values (deviations from the modern radiocarbon standard) for the radial samples displaying a small spread ranging from 130 to 200 per mil. The data are consistent with carbon cycling based on growth patterns involving replacement and fusion of areoles within the thallus as well as or instead of cellular or molecular replacement. Consequently, lifespan estimates cannot be obtained from 14C/C measurements of this species and the Δ14C profiles provide no insights into whether the relationship between size and age is linear or curvilinear in this species.

Natural Abundances of Carbon Isotopes (14C,13C) in Lichens and Calcium Oxalate Pruina: Implications for Archaeological and Paleoenvironmental Studies

“…The results suggest there is not a statistically significant difference in the Table 3 Average radiocarbon (∆ 14 C) data from lichens analyzed in this study and reported by Bench et al (2001Bench et al ( , 2002 Table 5. The data provides no evidence of a significant difference between the δ 13 C values for the Caloplaca and Lecania species when comparing their isolated calcium oxalate pruina separated from the lichen tissues, the lichen tissues themselves, nor the δ 13 C tis − δ 13 C ox differences for the 2 species.…”

“…Moreover, the 14 C values from the limestone samples are consistently greater than values obtained by Bench et al (2001;2002) from analyses of Caloplaca trachyphylla (mean 14 C = 175.8 ± 70.5‰) growing on sandstone and Rhizocarpon geographicum (mean ∆ 14 C = 152.6 ± 19.8‰) growing on siliceous rocks (Table 3). Thus, the limestone specimens have more atmospheric carbon that must have been incorporated during an earlier period when the atmospheric 14 CO 2 concentration was higher (due to bomb 14 C production).…”

“…Then, if substrate carbon was incorporated in the oxalate the 14 C/C of the limestone species would be lower (smaller ∆ 14 C values) and the 13 C/C higher (less negative δ 13 C values) compared to the lichens growing on the sandstone. However, as Bench et al (2001Bench et al ( , 2002 recently demonstrated, there is considerable internal carbon recycling and/or carbon turnover in the 2 lichens they studied. Such processes would cause a discrepancy between the contemporary atmospheric 14 C record and the 14 C content of the organisms, and limit our ability to predict the relative amount of carbonate carbon, if any, included for the production of oxalate.…”

“…Thus, the limestone specimens have more atmospheric carbon that must have been incorporated during an earlier period when the atmospheric 14 CO 2 concentration was higher (due to bomb 14 C production). This could be due to inclusion of older portions of the lichens during the sampling/scraping process or that the recent growth includes considerably more recycled carbon, a phenomenon demonstrated by Bench et al (2001;2002) for the 2 lichen species they studied.…”

Growth of crustose lichens: a review

“…The levels of the three carbohydrates were present at much higher concentration in the areolae than in the hypothallus which suggests that restriction of transport from areolae to hypothallus as hyphae age might be one explanation for the decreasing growth of larger R. geographicum thalli. Studies of C-14/C profiles across thalli of R. geographicum using mass spectroscopy, however, have provided little information to explain the growth curve (Bench et al 2001). The profile across thalli was flat and with little spread.…”