Use of ¹⁴C/C Ratios to Provide Insights into the Magnitude of Carbon Turnover in the Crustose Saxicolous Lichen Caloplaca Trachyphylla

Abstract

Abstract14C/C ratios in samples from radial transects across individual thalli of Caloplaca trachyphylla collected at two sites were measured and the results used to investigate whether 14C/C data might provide some insight into the magnitude of carbon turnover in this lichen species. The 14C/C data suggest that significant internal recycling/translocation of carbon is unlikely in the sampled thalli. However, converting the 14C/C data for the larger intact thalli sampled at each site to calendar years, using the atmospheric ⊃14C record, does not yield constant or even monotonically varying growth rates. Since crustose lichen growth rates are constant or decrease with thallus size, and since the 14C/C data from these larger thalli show a relatively small spread in 14C/C data values compared to the Northern Hemisphere atmospheric ⊃14C record over the past 50 years, the 14C/C data suggest that carbon turnover may be occurring. Carbon turnover was modelled starting with the atmospheric ⊃14C record. Turnover was incorporated so that for each year in the record a constant percentage of the total carbon was lost annually and replaced by new photosynthetically fixed carbon with a 14C/C ratio equal to that of the contemporary atmosphere. The 14C/C data from the radial samples were then converted to a calendar year using the model record. Constant annual carbon turnover values of 0, 0·5, 1, 1·5, 2, 2·5, 3, 3·5, 4, 4·5, 5, 5·5, 6, 7, 8, 9, 10, 15, 20, 25 and 50% were modelled. Carbon turnover values between 3 and 6% created ⊃14C model records that when applied to 14C/C data from the thalli produced constant radial growth rates that were: (1) identical for all lichens at a given site, and (2) independent of lichen size at a given site. The 14C/C data further indicate that annual carbon turnover in this species of lichen is <10%, independent of the nature of thallus radial growth. The data and modelling suggest that carbon turnover might provide a simple explanation for the 14C/C data from the thalli and might explain the discrepancies between the standard atmospheric ⊃14C record and the 14C/C ratios observed in C. trachyphylla.

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).…”

“…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.…”

“…In fact, the data contained in Table 2 suggest that the average ∆ 14 C values for lichen growing on limestone is at least 11.7‰ higher than the average ∆ 14 C for lichen growing on sandstone. A comparison of the ∆ 14 C values for the limestone species (Table 2) with those for Rhizocarpon geographicum growing on siliceous rocks (Bench et al 2001) and Caloplaca trachyphylla growing on sandstone (Bench et al 2002) was carried out utilizing two-sample t-tests with a Bonferroni correction (Bonferroni 1936;Miller 1981). The results suggest that the average ∆ 14 C values for lichen growing on limestone is at least 12.5‰ higher than the average ∆ 14 C for lichen growing on silica, and that there is no significant difference between the ∆ 14 C values for the limestone and sandstone substrates.…”

Growth of foliose lichens: a review

“…As a consequence, any translocation towards the lobe tip would be against a significant concentration gradient. More direct studies of translocation employing C-14/C ratios in radial transects across lichens (Bench et al 2002) also suggest that significant internal recycling and translocation of carbon is unlikely. Hence, factors other than the movement of carbohydrate may be necessary to explain the growth ratesize curves of foliose lichens.…”