Kaolinite and calcite foliar treatments induce physiological changes in cherry tree leaves

Foliar particle treatments can improve plant stress tolerance, but the underlying mechanisms remain unclear to date. In this study, the effect of supplying calcite and kaolinite was evaluated by treating leaves of field-grown cherry trees (Prunus avium var. Sweetheart) and evaluating their effects. Leaves were dipped in 5, 10 or 15% (w/v) calcite and kaolinite suspensions of similar particle size. Stomatal conductance (Gs), leaf temperature (Tleaf) and chlorophyll fluorescence were regularly monitored, while leaf mineral elements were determined at the end of the experimental period. The surface features, wettability and surface free energy of adaxial and abaxial leaf surfaces were characterised. Foliar kaolinite treatments increased tissue aluminium (Al) and silicon (Si) concentrations, with minor calcium (Ca) increments associated with calcite application. In addition, mineral particle supply changed the leaf concentration of other elements, such as potassium (K), magnesium (Mg), sulphur (S), boron (B), iron (Fe) or manganese (Mn). Chlorophyll fluorescence was not affected by the treatments, but short-term effects on Gs and Tleaf lasting only for few days after foliar application, were recorded. The supply of particle suspensions with surfactant, led to higher Gs values, while Tleaf generally decreased only for few days after foliar application. It is concluded that foliar particle treatments may trigger beneficial physiological changes after being exposed to transient stress situations, but further investigations are required for improving their effectiveness.