Does Diversity in Species Specific Leaf Traits Promote Stability of Forest Ecosystem Carbon and Water Fluxes?

Leaf functional traits exert strong controls on the exchange of carbon and water between terrestrial ecosystems and the atmosphere. It is often assumed that diversity in leaf traits promotes stability of ecosystem carbon and water fluxes. However, appropriate characterization of leaf functional trait diversity to test this assumption in forests remains a challenge, because leaf traits vary across species as well as through time and space within forest canopies. To assess the influence of functional trait diversity on ecosystem carbon and water fluxes, we measured leaf structural, chemical, and physiological traits for three codominant species (Acer rubrum, Quercus rubra, Pinus strobus) in a temperate forest stand within the footprint of an eddy covariance flux tower in southern New Hampshire, USA. Leaf traits were measured vertically through the canopy and temporally across the growing season and compared to eddy covariance derived estimates of stand-level carbon and water fluxes. Leaf structural and physiological traits varied across species, space, and time. For example, the date at which maximum leaf level photosynthesis was attained varied by more than six weeks across species and was strongly linked to leaf phenology and leaf structural development. The complementarity observed in the phenology of photosynthetic capacity as well as other leaf functional traits, highlight possible mechanisms that could regulate the stability of ecosystem carbon and water fluxes.