A comparison of stomatal traits between contemporary and fossil leaves of Melaleuca quinquenervia: Do they reflect climate variation?

Abstract

Stomatal traits have been shown to vary in predictableways in response to environmental change inmany plant species. As a consequence, stomatal traits in fossil leaves are sometimes used as proxies for past CO2 and climate. Herewe investigate the influence of temperature, rainfall and CO2 on stomatal traits in plant cuticle fine details of Melaleuca quinquenervia.We use both modern and fossil leaves deposited over the last c. 7500 years to evaluate the effect of CO2, and modern leaves for climate variables. We found a significant negative relationship between stomatal size and density across both modern and fossil leaves of M. quinquenervia. However, wewere unable to find any relationship between stomatal traits and CO2 across a range from 260 to 380 ppm. We were unable to find any robust relationships between stomatal traits and either evaporation or temperature using the modern dataset. Apogeotropic roots account for the lack of stomatal anatomy response to evaporation in sites that experiences inundation.Weconclude that stomatal size is a highly plastic trait in this species and changes do not necessarily reflect functional changes in the leaves.