Silicon Application Enhances Drought Tolerance in <i>Ficus annulata</i> by Improving the Physiological Responses and Chlorophyll Fluorescence Parameters

Drought and global warming affect the photosynthesis and various physiological processes of plants in Asian forest ecosystems. Improving physiological responses is the best way to overcome challenges to survival under drought and higher temperatures. This study was conducted to appraise the role of silicon (Si) in enhancing the drought tolerance and chlorophyll fluorescence response in banyan trees (Ficus annulata) in a pot experiment for 18 days. Three treatments were tested: control (CF), drought (DT), and drought stress sprayed with Si (DS). At the end of the trial, Si foliar spray at a concentration of 15 mM significantly increased (P < 0.05) the leaf relative water content (RWC) by 90%, total chlorophyll by 3.3 mg·g−1 FW, photosynthetic rate by 6.7 μmol CO2·m−2·s−1, stomatal conductance by 0.26 mol H2O·m−2·s−1, and transpiration rate by 2.7 μmol H2O·m−2·s−1. Moreover, ABS/RC, DIo/RC, TRo/RC, and ETo/RC were significantly lower than those under drought stress, while Fv/Fm and Pi were substantially higher than those under drought stress (P < 0.05). The levels of hydrogen peroxide (H2O2) production, electrolyte leakage (EL), and malondialdehyde (MDA) were considerably reduced during the drought stress experiment with Si spraying (P < 0.05). Foliar Si spraying did not enhance TSS content, but positively affected proline content (P > 0.05). The findings suggest that Si supplementation effectively improved the physiological responses, photosynthetic pigment content, and photochemical efficiency of F. annulata under drought conditions.