Effects of foliar and root silicon application on mitigating water deficit stress in young Eucalyptus urophylla plants

Abstract Background and Aims Water restriction significantly affects the growth and survival of young plants following transplantation. Although silicon (Si) is not typically considered essential for plants, it can help mitigate abiotic stresses. We hypothesized that Si application in plants, depending on how it is applied, can improve the tolerance to water restriction. The objective was to investigate how applying Si to the leaves and roots of young Eucalyptus urophylla plants can mitigate water restriction effects. Methods A greenhouse experiment was conducted with one factor consisting of three Si application methods (via root substrate, foliar spray, and a combination of both) and a control group with no Si; the other factor involved well-watered and water-deficit irrigation regimes, based on 90% and 30% pot capacity, respectively. Results Silicon application improved the plant’s tolerance to water restriction by maintaining stable cell turgor and increasing intrinsic water use efficiency. Silicon also helped to reduce stomatal conductance and water losses through transpiration, which prevented a decline in CO2 assimilation and promoted osmoregulation. It also prevented a decrease in chlorophyll content and attenuated oxidative stress, by increasing superoxide dismutase and guaiacol peroxidase activity, which contributed to preventing an increase in lipid peroxidation and electrolyte leakage. The effectiveness of Si supply was higher when applied through the roots or a combination of roots and leaves compared to foliar spray alone. Conclusion These findings suggest that Si application can be a useful strategy for improving plant tolerance to water restriction, particularly when applied through the roots.