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

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 (g,) 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 (Psipi(FT)) and at the turgor loss point (Psipi(TLP)), 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 (epsilon(MAX)) by 6.6 +/- 0.7 MPa. There were no clonal differences in either OA or elastic adjustment. Water stress increased significantly turgor potential at full turgor (Psi(FT)), 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 epsilon(MAX) during 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 epsilon(MAX) and Psipi(FT) 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.