Estimates of the diffusion resistance of some large sunflower leaves in the field.

Studies were made of resistance to gaseous exchange between large sunflower leaves and the bulk air in a crop canopy. Two components of the diffusive pathway for mass and sensible heat were evaluated; A) the resistance from the interior of the leaf to the leaf surface, and B) the resistance from the surface of the leaf through the leaf boundary air layer to the bulk air.IT WAS FOUND THAT: A) leaf resistance not only displays diurnal trends but shorter fluctuations, and B) boundary air layer resistance was significantly smaller than predicted from classical boundary layer formulae.