Lq. Chen et al., Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change, AM J BOTANY, 88(7), 2001, pp. 1309-1315
The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to E
arly Cretaceous) have been investigated to test whether these plant fossils
provide evidence for CO2-rich atmosphere in the Mesozoic. We first assesse
d five sources of natural variation in the stomatal density and index of ex
tant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. ful
ly developed leaves, (3) short shoots vs. long shoots, (4) position in the
canopy, and (5) male vs. female trees. Our analysis indicated that some sig
nificant differences in leaf stomatal density and index were evident arisin
g from these considerations. However, this variability was considerably les
s than the difference in leaf stomatal density and index between modern and
fossil samples, with the stomatal index of four species of Mesozoic Ginkgo
(G, coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower
than the modern values recorded in this study for extant G. biloba. Calcula
ted as stomatal ratios (the stomatal index of the fossil leaves relative to
the modern value), the values generally tracked the CO2 variations predict
ed by a long-term carbon cycle model confirming the utility of this plant g
roup to provide a reasonable measure of ancient atmospheric CO2 change.