Leaf orientation and light interception by juvenile Pseudopanax crassifolius (Cunn.) C. Koch in a partially shaded forest environment

• Published in: Oecologia 1995-11, Vol.104 (3), p.363-371
• Main Authors: Clearwater, M.J, Gould, K.S. (Auckland Univ. (New Zealand). School of Biological Sciences. Plant Sciences Group)
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; ARALIACEAE; Autoecology; Azimuth; BESOIN EN LUMIERE; Biological and medical sciences; BOSQUES; CANOPY; COUVERT; CUBIERTA DE COPAS; Declination; Diffuse light; FEUILLE; Forest canopy; FORESTS; FORET; FOTOSINTESIS; Fundamental and applied biological sciences. Psychology; Hemispherical photography; HOJAS; Leaf angle; Leaf orientation; LEAVES; Light; Light interception; LIGHT REQUIREMENTS; NECESIDADES DE LUZ; OMBRAGE; PHOTOSYNTHESE; PHOTOSYNTHESIS; Photosynthetically active radiation; Phyllotaxis; Plants; Plants and fungi; PLANTULAS; PLANTULE; Pseudopanax crassifolius; Quadrants; SEEDLINGS; SHADING; UMBRIA
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00328372

Leaf orientations and light environments were recorded for 40 juvenile Pseudopanax crassifolius trees growing in New Zealand in a partially shaded, secondary forest environment. Efficiencies of interception of diffuse and direct light by the observed leaf arrangments were calculated relative to those of three hypothetical leaf arrangements. Canopy gaps above the study plants were unevenly distributed with respect to azimuth and elevation above the horizon. Our results indicate that photosynthetically active radiation (PAR) received from the sides is more important than that received from directly above. In 33 of the plants leaf orientation was found to be significantly clustered towards one azimuth. The mean azimuth and the mean angle of declination were different for each plant. Leaves were steeply declined, and oriented towards the largest canopy gap at each site. Steep leaf angles reduced interception of direct and diffuse PAR when compared to interception by plants with a hypothetical horizontal leaf arrangement. When compared to a hypothetical arrangement with steep leaf declination and a uniform azimuth distribution, the observed leaf arrangement increased the efficiency of interception of diffuse PAR, but had a variable effect on the interception of direct PAR. Results indicate that the developing leaves of juvenile P. crassifolius orient towards the strongest sources of diffuse light, regardless of their value as a source of direct light. By maximising diffuse light interception while reducing direct light interception, leaf orientation may be a partial determinant of the types of habitats exploited by this species. This study emphasises the importance of considering diffuse light interception for plants growing in partially shaded environments.