Stable carbon isotope analysis of Cedrus atlantica pollen as an indicator of moisture availability

Benjamin A Bell,William J Fletcher,Peter Ryan,Helen Grant,Rachid Ilmen

doi:10.1016/j.revpalbo.2017.04.008

Abstract

Stable carbon isotope analysis of pollen provides potential for reconstruction of past moisture availability in the environment on longer time-scales compared to isotope analysis of plant tissue. Here we show that the carbon isotopic compositions (δ13C) of pollen, sporopollenin, leaf and stem tissues of Cedrus atlantica are strongly related. Untreated pollen δ13C has a significant linear relationship with sporopollenin δ13C (r2=0.97, p<0.0001) which is relatively depleted in 13C by an average 1.5‰. Carbon isotope discrimination (Δ13C) by sporopollenin (derived from pollen δ13C values) is related to mean annual (r2=0.54, p<0.001) and summer precipitation (r2=0.63, p<0.0001). A 100mm increase in mean annual precipitation results in sporopollenin Δ13C increasing by 0.52‰, or by 1.4‰ per 100mm summer precipitation. There is a stronger relationship between sporopollenin Δ13C and long-term annual scPDSI (r2=0.86, p<0.0001) and summer scPDSI (r2=0.86, p<0.001) aridity indexes, with reduced Δ13C as aridity increases. These relationships suggest that stable carbon isotope analysis of C. atlantica fossil pollen could be used as a quantitative proxy for the reconstruction of summer moisture availability in Northwest Africa.

Highlights

The stable carbon isotope composition (δ13C) of plant tissue is well understood as discrimination against 13C that occurs during photosynthesis (Park and Epstein, 1960; O'Leary, 1981; Farquhar et al, 1989)
Untreated pollen δ13C values are on average 1.5‰ less negative than sporopollenin, 1.7‰ than leaf and 0.9‰ than stem
The smallest differences in δ13C values are observed between sporopollenin and leaf, with sporopollenin δ13C averaging 0.2‰ less negative values; a slightly larger difference is observed between sporopollenin and stem, with stem averaging 0.7‰ more negative values than sporopollenin δ13C (Fig. 3)

Summary

Introduction

The stable carbon isotope composition (δ13C) of plant tissue is well understood as discrimination against 13C that occurs during photosynthesis (Park and Epstein, 1960; O'Leary, 1981; Farquhar et al, 1989) It can be used for a range of applications including determining photosynthetic pathways (Tieszen et al, 1979; Farquhar, 1983; O'Leary, 1988), inferring plant physiological differences (Francey et al, 1985; Körner et al, 1991), water-use efficiency (Farquhar and Richards, 1984; Marshall and Zhang, 1994; Warren et al, 2001) and for reconstruction of atmospheric and climate conditions of past and present environments (Feng and Epstein, 1995; Dawson et al, 2002).

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