Comparison of individual and combined effects of salinity and deficit irrigation on physiological, nutritional and ornamental aspects of tolerance in Callistemon laevis plants

The effect of water deficit, salinity and both applied simultaneously on several physiological and morphological parameters in the ornamental plant Callistemon laevis was studied to identify the tolerance mechanisms developed by this species to these sources of stress and to evaluate their adaptability to such conditions. C. laevis plants were grown in pots outdoors and subjected to four irrigation treatments lasting ten months: control (0.8 dS m−1, 100% water holding capacity), water deficit (0.8 dS m−1, 50% of the amount of water supplied in control), saline (4.0 dS m−1, same amount of water supplied as control) and saline water deficit (4.0 dS m−1, 50% of the water supplied in the control). Water and saline stress, when applied individually, led to a reduction of 12% and 39% of total biomass, respectively, while overall plant quality (leaf color and flowering) was unaffected. However, saline water deficit affected leaf color and flowering and induced an excessive decrease of growth (68%) due to leaf tissue dehydration and a high leaf Cl and Na concentration. Biomass partitioning depended not only on the amount of water applied, but also on the electrical conductivity of the water. Water stress induced active osmotic adjustment and decreased leaf tissue elasticity. Although both Na and Cl concentrations in the plant tissues increased with salinity, Cl entry through the roots was more restricted. In plants submitted to salinity individually, Na tended to remain in the roots and stems, and little reached the leaves. However, plants simultaneously submitted to water and saline stress were not able to retain this ion in the woody parts. The decrease in stomatal conductance and photosynthesis was more marked in the plants submitted to both stresses, the effect of which decreased photosynthesis, and this together with membrane damage delayed plant recovery. The results show that the combination of deficit irrigation and salinity in C. laevis is not recommended since it magnifies the adverse effects of either when applied individually.