CONICET | Buscador de Institutos y Recursos Humanos

A close examination of axis differentiation is key to the understanding of plant architecture and its ecologicalconsequences. The present study was aimed at evaluating the relationship between shoot size/structure andshoot growth dynamics in Luma apiculata (Myrtaceae), a widely distributed and cultivated but little investigatedAndean-Patagonian woody species. We assessed (a) organ preformation in apical buds, (b) shoot growth throughrepeated observations of labeled axes, (c) axillary production, leaf area, stem volume, dry mass of leaves, stemand reproductive structures, and allometric relationships for annual shoots of different sizes. The number ofpreformed organs in apical buds of L. apiculata averages seven nodes and exhibits little variability, in contrastwith the highly variable growth period (from few weeks up to more than six months) and the size reached byannual shoots. The leaf area/stem volume ratio increased more sharply during shoot extension in short than inlong shoots. Stem thickness was proportionally higher than other shoot-size measures in short shoots and longshoots as compared to intermediate-size shoots. Both the presence and the position of branches along shootsvaried notably with shoot size. Proportional mass and meristem allocation to fruit production decreased withshoot size. Unlike many other broadleaved temperate and temperate-cold tree species so far studied, the sizereached by L. apiculata shoots developed in the same year varies notably among axes in the same topologicalposition, and seems to depend largely on the expansion of non-preformed organs. A low dependency of shootgrowth on organ preformation may increase plasticity in axis structure, at the cost of a less hierarchical (moreshrubby) architecture. Simultaneous organ differentiation and expansion may allow plants to fine-tune shootstructure to the prevailing conditions during the growing season, and represent an advantage whenever conditionsfavourable for growth exhibit high between-year variations.

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