From buds to litter: seasonal changes in leaf wax concentrations and carbon isotopes and implications for the geologic past

Abstract:

The carbon isotope composition (δ¹³C) of leaf waxes, such as n-alkanes, have extensively been used in paleoenvironmental studies for reconstruction of the past vegetation, climate and carbon cycling. There is however little information available on the seasonal variation of leaf wax concentration and δ¹³C in modern plants and when the δ¹³C signal is set. This lack of information confounds interpretations of leaf wax δ¹³C in sedimentary archives. To address this gap, this study investigates temporal changes in n-alkane and n-alkanoic acid δ¹³C values in several species (Acer rubrum, Acer saccharum, Ulmus Americana, Sassafras albidum, and Juniperus virginiana) within a single temperate deciduous forest stand in southern Ohio. We sampled atmospheric air, buds, leaves, leaf litter, and surface soil weekly during leaf flush and biweekly thereafter. In A. rubrum, A. saccharum, and U. Americana, buds had one or two dominant n-alkanes, such as C₂₉ and C₃₁. After leaf flush, the concentrations of shorter n-alkanes (C₂₃~C₂₇) significantly increased relative to the longer chain-lengths. We are currently analyzing remaining samples from the growing season and are analyzing bulk leaf and leaf wax (n-alkanes, n-alkanoic acids) δ¹³C values. This information will be important for identifying environmental and physiological controls on leaf wax δ¹³C and will improve interpretations of leaf wax δ¹³C preserved in the geologic record.