Plasticity of Aesculus Glabra (Hippocastanaceae) Leaf Traits Along Small-Scale Light Gradients within Forest Stands

Abstract

Phenotypic plasticity in response to environmental heterogeneity is an important adaptive
component of plant strategies. This study addresses plasticity of Aesculus glabra leaf traits in response to
small-scale (within-canopy, within-stand) gradients of light availability in a temperate deciduous forest. Leaf
mass per area, stomatal density, stomatal length, water content, leaf life span, and chlorophyll content were
measured in two populations in northern Indiana. Light availability was determined through hemispherical
canopy photography. Stomatal density, leaf mass per area, and leaf life span were positively correlated with
light availability (r = 0.51, p < 0.001; r = 0.51, p < 0.001; r = 0.37, p = 0.02, respectively). Chlorophyll
content on an area basis and water content were negatively correlated with light availability (r = −0.49, p <
0.002; r = −0.58, p < 0.001, respectively). Most correlations of these leaf characteristics with each other
were significant. Chlorophyll content on a mass basis and stomatal length did not correlate with light
availability. Leaf life span was longer in branches at the top of the crown than in self-shaded lower branches.
Leaf traits in this species show significant plasticity in response to small-scale gradients of light availability.
The increase in leaf lifespan with increasing light is atypical, and may be due to poor carbon balance of A.
glabra under shaded conditions. Since this species leafs out before the canopy does, it is unclear how it
perceives and responds appropriately to the full-canopy light environment.