Bench, G., Clark, B. M., Mangelson, N. F., Clair, L. L. St., Rees, L. B., Grant, P. G. and Southon, J. R. (2002) Use of 14C/C Ratios to Provide Insights into the Magnitude of Carbon Turnover in the Crustose Saxicolous Lichen Caloplaca Trachyphylla. The Lichenologist, 34 (02). pp. 169-179. DOI 10.1006/lich.2002.0377.

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Abstract

14C/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.

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