Controls on leaf breakdown rates along inundation gradients in perennial Appalachian stream ecosystems

Changes to water availability potentially affect important ecosystem functions such as in-stream organic matter processing. Although organic matter dynamics in intermittent streams have been well-studied, we address a similar issue in perennially wet systems in the Coweeta Hydrologic Lab in North Carolina. Red maple (Acer rubrum L.) and white oak (Quercus alba) leaf packs were allowed to decompose over a 6-month period in four site types representing a gradient of inundation:  experimentally reduced surface flow, normal stream flow, bank-side, and up-slope terrestrial.  Although overall rates were not different for either red maple or white oak, the influence of winter storms altered the overall trajectory of decomposition for both leaf types. Colonization by different microbial assemblages appeared to influence leaf decomposition initially (in addition to altering leaf stoichiometry), but the overall effect of storms appeared to homogenize biotic influences in latter stages of decomposition for leaves in the two in-stream sites. In contrast, decomposition rates and biotic influences were similar for bank and terrestrial sites for both leaf species. These data suggest that the timing and intensity of storms may be a strong control over leaf decomposition, possibly overriding any biotic effects typically associated with organic matter processing in stream ecosystems.