Influence of Morphometric Characteristics of the Hybrid Walnut Tree (Juglans nigra x Juglans regia) Crown on its Radiative Balance

摘要

The effects of leaf geometry on radiative transfer were examined on four 8-year-old Juglans nigra x Juglans regia trees. The woody architecture of the trees was obtained by in situ 3D digitizing whereas the size and orientation of leaves were determined from a sample. Through the AMAPmod software we could then reconstruct 4 virtual trees used as a support for radiative transfer computation We analysed the influence of (ⅰ) digitizing accuracy, (ⅱ) leaf area, (ⅲ) leaf insertion angle and (ⅳ) leaflet angle on the estimation of intercepted PAR by the canopy and of leaf irradiance. Results showed that the effect of a +- 5 cm digitizing inaccuracy was weak at the canopy scale but could reach 12% of intercepted PAR at the intra-canopy scale. Leaf area was the tested parameter which influenced most intercepted PAR by the canopy. Taking the leaf area distribution into account on the long shoots slightly affected intercepted PAR in our case. Leaf and leaflet inclinations had a more limited effect on the radiative transfers considered at the whole canopy scale but responses varied between the four trees. Our results suggest that leaf and leaflet inclination measured on the real trees optimise intercepted PAR by the canopy although the four trees did not present the same architecture.