Salt Spray and Surfactants Induced Morphological, Physiological, and Biochemical Responses in Callistemon citrinus (Curtis) Plants

The growth and aesthetic value of ornamental plant species used near coastlines are negatively influenced by salt spray. The presence of surfactants could enhance salt damage. To analyze the influences of salt spray and surfactants alone and in combination with each other, individual Callistemon plants were subjected to different treatments for 8 weeks: a solution simulating the composition of seawater (salt spray), a solution containing an anionic surfactant (surfactant), a solution with salt spray and anionic surfactant (salt plus surfactants), and deionized water (control). To study the influence of different climatic conditions, two growing periods, from January to March (I CP) and from May to July (II CP), were established. Salt spray, alone or with surfactant action, influences plants’ growth and aesthetic features in different cycle periods. The percentage of leaf damage significantly increased with salt spray and salt plus surfactants during II CP (~27%). Additionally, the Na⁺ and Cl⁻ contents were enhanced in the leaves in both CPs, but the contents in the roots were only enhanced in the II CP. The gas exchanges were significantly influenced by the treatments, especially during the II CP, when a reduction in net photosynthesis due to salt spray was observed starting from the second week of stress. At the end of the experiment, in both cycle periods, the leaf proline content increased in the salt spray and salt plus surfactants treatments. In both CPs, PCA revealed that the morphological and physiological parameters were directly associated with the control and surfactants treatments, whereas the mineral contents and biochemical parameters were directly correlated with the salt and salt plus surfactants treatments. The additive effect of surfactant stress, compared to salt stress, did not appear to be significant, with the exception of CP II, and for some parameters, the solubilization action of surfactants was favored by higher temperatures.