Water relations in eucalypt seedlings as affected by potassium levels and water stress were studied under controlled conditions. In a first trial, two levels of K (0 and 150 mg L -1) and two levels of soil moisture (field capacity and cyclic water stress) were tested on seedlings of eucalypt hybrids grown in plastic bags containing 9 L of a redyellow latossol. The hybrids reacted differently according to K and soil moisture level combinations.
In a second trial, the effect of K level of a nutrient solution on water relations of eight eucalypt species was investigated. It was observed that a greater K level (70 mg L-1) in the nutrient solution increased the efficiency of water use (EWU) of all eucalypt species, particularly of Eucalyptus camaldulensis and E. citriodora which when supplied with less K (7 mg L-1) showed lower EWU and a higher transpiration rate than E. tereticornis, E. grandis and E. pellita.
In a third trial, polyethylene glycol (PEG) was added to the nutrient solution in order to obtain three osmotic potentials (that corresponding to the original nutrient solution; -0.25 MPa; -0.50 MPa). The results allowed the placement the eucalypt species into three groups according to the stomatal resistance (r): 1) E. camaldulensis, E. tereticornis, and E. citriodora which showed the smallest r-values, ranging from 2.94 to 3.99 s*cm-1; 2) E. pellita, E. cloeziana, and E. grandis with intermediate r-values ranging from 5.65 to 11.09 s*cm-1 ; and 3) E. urophylla and E. saligna with r-values of 20.70 and 26.98 s*cm-1.