Photosynthesis by grapevine canopies.
A new field technique to estimate photosynthesis is described. It relies on describing direct and diffused light fluxes within the canopy, and photosynthesis is then estimated by reference to a light response curve. An analysis of grapevine canopies indicated that most photosynthesis is due to exterior leaves absorbing direct light. Levels of diffused light within dense canopies are very low, thus inhibiting photosynthesis. Owing to high insolation and the light saturation level of photosynthesis, overall efficiency is low. The implications of altered leaf-sun angle are considered as a means of improving this efficiency.