The Effect of Leaf Flutter on the Flux of CO 2 in Poplar Leaves

Theoretical equations and experimental data were utilized to examine the effect of leaf flutter on the CO 2 -exchange characteristics of two species of poplar (aspen, Populus tremuloides and cottonwood, Populus fremontii). In order for bulk flow to enhance CO 2 flux substantially, the pressure gradient created by leaf flutter would have to be greater than the pressure gradient across a fixed leaf normal to the flow, which was shown to be unlikely. As aspen has hypostomatous leaves, and therefore low permeability coefficients, bulk flow would be even less important for CO 2 flux in aspen than in cottonwood. Leaf flutter may increase the boundary-layer conductance to CO 2 by as much as 20-60% over constrained leaves in laminar flow (...)