XVI International Botanical Congess

Leaf area of sunflower is highly variable even in the absence of stresses, and closely related to intercepted radiation. A 3D model interacting with the environment and comprising ecophysiological modeling aims to simulate this effect. A two-phase model of leaf expansion is used, with an exponential expansion followed by a slow down of expansion rate. A temporary decrease in intercepted radiation only affects leaves in exponential phase, but causes delayed reductions in expansion rate during the whole leaf development. This in turn causes a reduction in intercepted radiation and a further decrease in leaf expansion of younger leaves. Architectural modeling, coupled with models of interception of incident radiation and multiple scattering within canopy is adequate for modeling this feed back process, and is tested in a series of field experiments.