Some Aspects of Tissue Water Relations in Three Populations of Eucalyptus Viminalis Labill.

SUMMARY Using the pressure bomb technique, measurements have been made of the tissue water relations of seedlings of three populations of Eucalyptus viminalis, and of adult shoots of trees from two contrasting sites, to facilitate an understanding of the physiological basis of intra‐specific variation in drought resistance. For both juvenile and adult material, the shoot water potential of the most drought resistant population declined most rapidly with decreasing water content. Estimates of the fraction of water in the cell walls at full turgor were also greatest for this population, averaging 0.36 for juvenile and 0.40 for adult material. Calculated values for the bulk modulus of elasticity of the walls were very variable, but tended to be higher, in adult than juvenile tissues. The results suggest that in dry habitats there has been selection for plants which, during temporary periods of drying, can maintain a water content above the critical level for cell damage. Differences between two very closely situated field populations emphasize the need to consider the role of edaphic as well as climatic factors in selection for drought resistance.