Bioindicator capacity of trees towards dryland salinity

To investigate plant–soil reactions towards site salinity we chose Ruprechtia triflora as the dominant tree species in its natural habitat in dry forests of Paraguay. We applied freezing point osmometry to measure tree leaves and soil samples identically on the basis of colligative solute properties. In order to substantiate the first field findings, the relation of tree and soil in terms of salinity was further investigated under controlled conditions in the greenhouse. R. triflora shows extreme osmotic adaptability. In three independent greenhouse experiments with NaCl application, Ruprechtia seedlings and later Eucalyptus dunnii seedlings from E Australia (for inter-species comparison) showed highly significant responses to their soil salinities. We conclude that tree leaves can serve as bioindicator for soil salinity within the tree’s rhizosphere.