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Bud and growth-unit structure in seedlings and saplings of Nothofagus alpina (Nothofagaceae)¹

Departamento de Botánica, Universidad Nacional del Comahue, Quintral 1250, 8400, Bariloche, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina; INRA, Unité Mixte de Recherche (UMR) Cirad-Cnrs-Inra-Ird-Université Montpellier 2, "botAnique et bioinforMatique de l'Architecture des Plantes" (AMAP), UMR T51 (CIRAD), UMR 5120 (CNRS), UMR 931 (INRA), M123 (IRD), UM27 (UMII) TA A-51/PS2, Boulevard de la Lironde, 34398 Montpellier, Cedex 5, France

ABSTRACT

In temperate trees, axis length growth generally results from the differentiation of organs at the end of a growing season and the extension of such "preformed organs" in the next growing season. Neoformation, i.e., the simultaneous differentiation and extension of organs, has been studied for only a few species. Here we evaluated bud composition and growth unit (GU) size for seedlings and saplings of Nothofagus alpina, a valuable South American forest tree. Trunk GUs of seedlings and saplings included preformed and neoformed organs, whereas main-branch GUs of saplings were entirely preformed. The size of a GU was more closely related to the number of preformed green leaves than to the number of cataphylls of its preceding bud. Proximal buds of a trunk GU had more cataphylls and less green-leaf primordia than distal buds. Individual leaf area increased from proximal to distal positions on trunk GUs. For trunk and main-branch GUs, the length/width ratio was maximum for leaves in intermediate positions. The development of large neoformed leaves at the end of the growing season could increase the photosynthetic capacity of this species in late summer, when the activity of preformed organs is likely to be decreasing.

Key Words: bud structure • growth unit • leaf size • neoformation • Nothofagaceae • Nothofagus alpina • Patagonia • preformation