American beech leaf‐litter leachate chemistry: Effects of geography and phenophase

The decomposition of broadleaved tree leaves can contribute a substantial amount of energy to forested watersheds via dissolved organic matter (DOM), nutrients, and biological activity. Less is known about how these inputs may vary within a single tree species that is known to have two genetically distinct and geographically separate populations, or how these inputs may change throughout autumn senescence and abscission. It is often implicitly assumed that intraspecific differences in leaf-litter leachate chemistry do not significantly differ geographically. We analyzed the morphological and chemical leaf traits and leachates from Fagus grandifolia (American beech) leaves (n = 360) during three phenophases: fresh green leaves, senescing leaves, and fallen leaves. During each phenophase, leaves were collected from four sites along a geographic transect stretching from Vermont to North Carolina (over 1400 km), with two sites representing each genetic population and differing climatic conditions. Leachates were analyzed for routine solutes and nutrients, as well as fluorescent and UV-visible absorbance indices. Amounts of macro- and micronutrients were highly variable among sites and phenophases but tended to be lowest during the fallen-leaf phase, while measured fluorescence and absorbance indices tended to increase during the senescing-leaf phase and plateau. Results suggest significant dif- ferences in leached nutrients among sites, and optical properties and nutrients among pheno- phases. Aromaticity and molecular weight of DOM in leachates was generally low, and aromatic- ity and humification of leachates both increased over time with leaf age. These results also sug- gest that geographically (or genetically) separate populations of the same species do not experi- ence senescence in the same way and that implicit assumptions of intraspecific uniformity of leaf-litter leachate chemistry for a given tree species may be invalid.