LAUSR

Abstract The hydrogen isotopic composition of leaf waxes ( δD wax ) primarily reflects that of plant source water. Therefore, sedimentary δD wax records are increasingly used to reconstruct the δD of past precipitation ( δD p ) and to investigate paleohydrologic changes. Such reconstructions rely on estimates of apparent fractionation ( e app ) between δD p and the resulting δD wax . However, e app values are modified by numerous environmental and biological factors during leaf wax production. As a result, e app can vary widely among plant species and growth forms. This complicates estimation of accurate e app values and presents a central challenge to quantitative leaf wax paleohydrology. During the 2014 growing season, we examined e app in the five deciduous angiosperm tree species ( Prunus serotina , Acer saccharinum , Quercus rubra , Quercus alba , and Ulmus americana ) that dominate the temperate forest at Brown’s Lake Bog, Ohio, USA. We sampled individuals of each species at weekly to monthly intervals from March to October and report δD values of n -C 29 alkanes ( δD n -C29 alkane ) and n -C 28 alkanoic acids ( δD n -C28 acid ), as well as xylem ( δD xw ) and leaf water ( δD lw ). n -Alkane synthesis was most intense 2–3 weeks after leaf emergence and ceased thereafter, whereas n -alkanoic acid synthesis continued throughout the entire growing season. During bud swell and leaf emergence, δD lw was a primary control on δD n -C29 alkane and δD n -C28 acid values, which stabilized once leaves became fully expanded. Metabolic shifts between young and mature leaves may be an important secondary driver of δD wax changes during leaf development. In mature autumn leaves of all species, the mean e app for n -C 29 alkane (−107‰) was offset by approximately −19‰ from the mean e app for n -C 28 alkanoic acid (−88‰). These results indicate that in temperate settings n -alkanes and n -alkanoic acids from deciduous trees are distinct with respect to their abundance, timing of synthesis, and e app values.