Silicon Application Methods Differentially Modulate Nutrient Uptake and Morphophysiology in Passiflora edulis Seedlings Under Salt Stress

Silicon (Si) is a beneficial element that alleviates the adverse effects of salinity in plants. Despite extensive evidence of Si-mediated stress alleviation in other crops, information for tropical fruit species such as Passiflora edulis remains limited, especially regarding the efficiency of different application methods. This study evaluated two yellow passion fruit cultivars (BRS Sol do Cerrado and BRS Gigante Amarelo) at the seedling stage under five management conditions: irrigation with 1.2 dS m−1 water (control), 4.0 dS m−1 water (salt stress), and salt stress combined with Si applied via soil, foliar spray, or both (soil + foliar), using silicic acid as the Si source. The experiment was conducted in a completely randomized design in a 2 × 5 factorial arrangement with five replicates. High salinity decreased foliar nutrient concentrations, gas exchange, and seedling quality, whereas Si mitigated these effects depending on the application method and cultivar. Combined soil and foliar application increased nutrient contents, biomass, and the Dickson Quality Index, especially in BRS Gigante Amarelo. These findings provide new insights into Si management for P. edulis and offer practical implications for improving nutrient balance, growth, and seedling performance under saline conditions.