Seasonal variations of leaf wax n-alkane molecular composition and δD values in two subtropical deciduous tree species: Results from a three-year monitoring program in central China

We investigated the seasonal variations of the molecular and hydrogen isotopic compositions of leaf cuticular n-alkanes (delta D-alk) in two subtropical deciduous tree species (Quercus chenii, Liquidambar formosana) over a three-year period. Average chain length values of long chain n-alkanes in both species are lower in young leaves than in mature ones. The delta D-alk values in both tree species show seasonal fluctuations that can be as large as 78% in a single year. The seasonal changes in molecular and isotopic compositions suggest that leaf wax n-alkanes in these subtropical deciduous tree species integrate environmental information over a large portion of the annual growth cycle in response to fluctuations in environmental stresses (e.g. storms, droughts). In addition, the changes reveal that seasonal patterns of delta D-alk can differ between different deciduous species at the same location and among different years. Spring leaves collected in 2014 had more negative delta D-alk values than those collected in 2015 and 2016, possibly responding to differences in annual precipitation D/H ratios and associated atmospheric circulation. These preliminary results highlight that extended seasonal monitoring of leaf wax delta D-alk values can improve their application to reconstructing paleohydrological histories. (C) 2018 Elsevier Ltd. All rights reserved.