Variación en atributos anatómicos asociados a la conducción y almacenamiento de agua, en tres poblaciones de Maihuenia poeppigii (Otto ex Pfeiff.) K. Schum. (Cactaceae) en un gradiente altitudinal

Variability in anatomical stem traits could be related with the environmental conditions where plants develop (e.g. low temperatures, drought, short growing season), and this variability reflects the ability of a species to be established in habitats that differ in these conditions. Maihuenia poeppigii (Otto ex Pfeiff.) K. Schum is not only one of the Cactaceae species with the southernmost distribution of America, but also presents populations along a wide range of altitudes (approx. from 15 to 2,600 masl.), where the climate varies greatly. This study evaluates the variability in stem anatomical traits related to xylem conduction (density, diameter and relative hydraulic conductivity of vessels) and to water storage (degree of succulence of stem and leaves), in three populations of M. poeppigii that are established in an altitudinal gradient in the South-Central Chile. Additionally, the maximum height of the M. poeppigii cushions was determined as a measure of its exposure to the environment. Average density, diameter and relative hydraulic conductivity of vessels differed significantly among populations from different altitudes. While vessel density and succulence of the stems increased in populations located at higher altitudes in the gradient, diameter of the vessels and plant height decreased. The succulence of the leaves did not differ among the three surveyed populations. The variation found in these anatomical traits reflects a differential strategy in the use and storage of water between the populations established in the altitudinal gradient. This pattern of functional responses can explain the ability of this species to occupy sites that differ in altitude.