Bud and shoot structure in seedlings and saplings of Nothofagus alpina (Nothofagaceae).

PUNTIERI JAVIER; GROSFELD JAVIER ; STECCONI MARINA; BRION CECILIA; BARTHÉLÉMY DANIEL

AMERICAN JOURNAL OF BOTANY

Botanical Society of America

Lugar: St. Louis; Año: 2007 vol. 94 p. 1382 - 1390

0002-9122

For tree species from temperate-cold regions, most of their axis length growth is generally achieved through the differentiation of organs at the end of a growing season and the extension of such organs (known as preformed organs) in the following growing season. Neoformation, i.e. the simultaneous differentiation and extension of organs, has been studied only for a very low number of species. In the present study, bud composition and its relation with growth-unit final size, plant developmental stage and position on the tree were evaluated for seedlings and saplings of Nothofagus alpina, a valuable forest tree from temperate South America. Trunk growth units of seedlings and saplings included preformed and neoformed organs whereas main-branch growth units of saplings were entirely preformed. The size of a growth unit was more closely related to the number of preformed green leaves per bud than to the total preformation of the bud (including cataphylls and green leaves). Proximal buds of a trunk growth unit had more cataphylls and less green-leaf primordia than distal buds. Although the area of individual leaves increased from proximal to distal positions on trunk growth units, the change in the area and length/width ratio of leaves between the preformed and neoformed growth-unit portions was less sharp than expected. 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.