Abaxial Leaf Illumination: A Strategy to Enhance Photosynthesis and Yield in strawberry (Fragaria × ananassa)

Low light intensity and short photoperiods during autumn and winter are frequently exacerbated by structural shading in protected cultivation systems, limiting strawberry ( Fragaria × ananassa ) yield. Although supplemental LED lighting is commonly used to mitigate low-light stress, it is typically directed at the adaxial leaf surface, overlooking the photosynthetic potential of the abaxial surface. In this study, we investigated the effects of directional supplemental lighting applied to adaxial and abaxial leaf surfaces at different intensities on leaf photosynthetic traits, stomatal morphology, fruit yield and quality. Results revealed that the abaxial surface exhibited lower baseline photosynthetic capacity; however, moderate-intensity supplemental lighting significantly enhanced CO₂ assimilation, fruit yield, and fruit quality, achieving outcomes comparable to those under high-intensity adaxial lighting. Plant growth was further promoted under supplemental abaxial illumination, with the adaxial surface exposed to ambient light. Notably, abaxial lighting is more energy efficient than adaxial lighting with equal photon flux. Our results demonstrate that abaxial supplemental lighting is a viable and energy-saving strategy for improving light use efficiency and fruit production under suboptimal light conditions, and provide new insights into leaf surface-specific photosynthetic responses, establishing a foundation for optimising light distribution in controlled agricultural environments. • Moderate abaxial supplemental light effectively promoted the yield of strawberries. • Moderate abaxial light boosts CO₂ assimilation, yield, and fruit quality. • Moderate abaxial lighting enables energy-saving strawberry cultivation.