FOLIAGE DETERMINANTS OF LIGHT INTERCEPTION IN SUNNY AND SHADED BRANCHES OF FAGUS-SYLVATICA (L.)

A 3D digitising device was used to acquire architectural information o n branches from open-grown and understory saplings of Fagus sylvatica (L.). Branch and shoot images were reconstructed from the data set usi ng an image synthesis software (freeware POV-Ray(R)). Image analysis e nabled us to: (i) quantitatively investigate light interception at the shoot and the branch scales; (ii) to derive relevant structural param eters at both scales; (iii) to relate the observed shift with light en vironment on the independent effects of leaf inclination, within-shoot shading, shoot density and dispersion within the branch. Leaf display pattern, both at the branch and the shoot scale, was strongly affecte d by light availability. At the shoot level, reduced self-shading in s haded conditions resulted in an increased light capture as high as 32% , expressed on a leaf area basis in the vertical direction. At the bra nch level, shaded environment caused a substantial increase of 60%. Co nsidering that incident irradiance varies by a factor of 20 between un derstory and open conditions, plasticity in branch architecture allows to reduce the discrepancy in the amount of intercepted light to a fac tor 12. This difference in light capture ability at the branch level w as shown to result from: (i) more horizontally inclined leaves in shad e; (ii) a greater branch leaf area index in sunny conditions (on avera ge 1.60 vs. 0.95 in shaded conditions); (iii) a more regular shoot dis persion in shade (shoot dispersion index averaged 1.30 vs. 1.10 in the open). Finally, results are discussed in terms of optimal architectur e for carbon gains, and the interest of the method for parameterisatio n of radiative transfer models is emphasised. (C) 1998 Elsevier Scienc e B.V.