Jorge Hugo Lemcoff

Elastic and osmotic adjustments in rooted cuttings of several clones of Eucalyptus camaldulensis Dehnh. from southeastern Australia after a drought

Summary Eucalyptus camaldulensis Dehnh., considered as a drought tolerant species, was examined in relation to some mechanisms linked to drought tolerance (cell-wall elastic adjustment and osmotic adjustment) and to the intraspecific variation related to those features. Rooted cuttings of five clones obtained from three different provenances from Australia (Gilgandra: 106, 109; Lake Albacutya: 119, 125; Condamine: 105) were gradually submitted to a water limitation regime. Water stress curtailed relative leaf area growth rate, pre-dawn relative water content (RWC) and noon stomatal conductance (gs) in all clones. Shoot water parameters were estimated at the end of the drought period by pressure-volume (P–V) analysis through a repeat pressurization method. The curves obtained were analyzed by Schulte’s P–V Curve Analysis Program. Drought decreased very significantly the osmotic potential at full turgor (χπFT) and at the turgor loss point (χπTLP), with a significant clone effect: 105 had the lowest values (–2.12±0.04 MPa and –2.39±0.05 MPa). Osmotic adjustment (OA) on average was 0.34±0.02 MPa. Drought increased maximum bulk modulus of elasticity (ɛMAX) by 6.60.7 MPa. There were no clonal differences in either OA or elastic adjustment.Water stress increased significantly turgor potential at full turgor (χFT), and differences between control and stress plants show that the OA recorded did not fully account for the positive changes in turgor of stressed plants. Drought decreased shoot turgid mass/dry mass ratio (TM/DM), again with a significant clone effect: 105 had the lowest value (2.66±0.11). Reduced shoot TM/DM combined with increases in ɛMAXduring stress were indicative of cell wall adjustment, reduced turgor-loss volumes and tightening of the cell walls around the protoplasts, suggesting a cell size reduction. No effects were observed on RWC at the turgor loss point. A regression model that considered ɛMAX and χπFT explained best the response patterns of stressed plants. The mechanisms observed in Eucalyptus camaldulensis that delay growth while maintaining turgor and water uptake allow us to consider it as a dehydration postponement species.

IMPACTO DEL ESTRÉS HÍDRICO Y LA PROCEDENCIA DE EUCALYPTUS GLOBULUS LABILL. SOBRE EL COMPORTAMIENTO DE HERBIVORÍA DE ACROMYRMEX LUNDI GUÉRIN

Las diferentes especies de hormigas aceptan la mayor parte de las plantas que se les ofrecen; sin embargo, ha sido probado cierto comportamiento selectivo y en plantas bajo estres hidrico se ha reportado mayor dano por su herviboria. Dos ensayos fueron llevados a cabo con la hormiga negra comun, sobre siete procedencias de tres subespecies de Eucalyptus globulus. Tales procedencias fueron ofrecidas en nido artificial en laboratorio y bajo estres hidrico, en nidos a campo. En laboratorio, la preferencia expresada como tiempo de acarreo fue significativamente diferente entre procedencias, aunque no entre subespecies. En campo, el area promedio removida fue significativamente mayor en plantas sometidas a estres hidrico. Este parecio incrementar la atraccion para las hormigas cortadoras, superando la preferencia relativa por las procedencias, manifestada en laboratorio. Por lo tanto, la utilizacion de procedencias menos preferidas es una alternativa de manejo solo en aquellas areas donde el estado hidrico puede ser controlado. La heterogeneidad del suelo causaria areas relativamente mas secas y tales situaciones localizadas de estres hidrico podrian tornar a ciertos individuos mas atractivos y, por lo tanto, mas danados.