Synergistic Effects of Supplemental Lighting and Foliar Phosphorus Application on Flowering in Passion Fruit (Passiflora edulis)

Passion fruit (Passiflora edulis), a commercially vital tropical crop, faces flowering instability due to photoperiod-sensitive flowering patterns, particularly under the cloudy, rainy climates of subtropical regions. To mitigate floral suppression during unfavorable light conditions, this study implemented a dual-modality strategy combining 16 h daily supplementary lighting (460 nm blue + 630 nm red spectrum) and foliar application of a high-phosphorus-containing nutrient, the Plant-Prod (nitrogen–phosphorus–potassium = 10:52:10) grown in field ‘Qinmi No. 9’. The treatment significantly stimulated lateral branch formation, internode elongation, flower retention, stage IV flower bud development, and enhanced photosynthetic efficiency. Physiological analyses revealed that the treatment increased the net photosynthetic rate (Pn), reduced the intercellular carbon dioxide concentration (Ci), and enhanced stomatal conductance (Gs), indicating the improvement of carbon assimilation. Controlled seedling trials further confirmed these effects, with treated groups exhibiting accelerated lateral branching and stress resilience. This integrated approach, combining optimized supplemental lighting and precision phosphorus fertilization, offers a practical and scalable strategy to stabilize passion fruit yields in climate-variable regions, with immediate potential for commercial orchards and greenhouse production.