Morphological and physiological components mediating the silicon-induced enhancement of geranium essential oil yield under saline conditions

Salinity stress impedes plant growth and productivity. In this study, the alleviating role of potassium silicate (K2SiO3) under saline conditions was addressed. Geranium plants were grown at three salinity levels (1.8, 4 and 6 ds/m by using NaCl), where K2SiO3 was weekly applied at different concentrations (0, 0.5 or 1 mM). Plant biomass, root volume, leaf pigment (chlorophyll, carotenoids) content and essential oil yield were assessed. Electrolyte leakage, lipid peroxidation, proline content, as well as antioxidant enzyme (catalase and peroxidase) activities were also evaluated. Increasing the salinity level from 1.8 to 4 ds/m, as well as from 4 to 6 ds/m, led to significantly smaller plants, with lower pigment content and reduced essential oil yield. Plants grown under more saline solution also suffered from increased electrolyte leakage and lipid peroxidation. These effects were related to decreased antioxidant enzyme activities. Weekly Si application not only significantly improved all assessed parameters under control conditions (1.8 ds/m), but also partly mitigated the above-mentioned effects under saline conditions (4 and 6 ds/m). This promotive effect of Si was more prominent when applied at 1 mM. Overall, the results show that weekly K2SiO3 application promotes productivity in geranium, in particular under saline stress.