Leaf carbon isotope compositions and stomatal characters: important considerations for palaeoclimate reconstructions

Variations in stable carbon isotope composition and stomatal characters of fossil leaves are being used increasingly to provide information about palaeoatmospheric CO2 concentrations. However, differences in these parameters are not solely dependant on CO2 concentrations and factors such as aspect (i.e. sun and shade) must be considered in palaeoenvironmental reconstructions. Stable carbon isotope analyses in combination with stomatal analyses of canopy sun and shade leaves of modern Fagus sylvatica reveal that sun leaves contain more 13C and have higher stomatal indices when compared with shade leaves. These observations, probably related to stomatal conductance, have significant implications for studies using fossil leaves to reveal palaeoclimate signals.