Photosynthetic light response (Pn–PAR) curves provide insights into optimizing light use efficiency and plant productivity while supporting decision-making on canopy management, such as plant spacing and pruning. In strawberry (Fragaria ×ananassa), previous Pn–PAR studies have primarily focused on mature leaves but ignored how photosynthetic capacity varies with leaf and plant age. To fill this knowledge gap, we examined leaf and plant age-related changes in Pn–PAR of strawberry plants. A field experiment was conducted with ‘Florida Brilliance’ short-day strawberry during the 2023–2024 growing season in West Central Florida. We determined Pn–PAR at three development stages: early (21 Nov.), mid (12 Dec.), and late (1 Feb.) growth stages. Leaves were classified into three categories based on leaf age: young (first fully expanded leaf), mature (fully developed leaf), and old (senescing leaf). Measurements were made using a portable infrared gas analyzer at ten photosynthetically active radiation (PAR) levels ranging from 0 to 2,000 μmol m⁻² s⁻¹ at a constant CO₂ concentration of 400 μmol m⁻² s⁻¹. During the early growth stage, the light-saturated photosynthetic rate (Pmax) was highest in mature leaves, followed by old and young leaves (18.17, 16.33, and 15.48 µmol CO₂·m⁻²·s⁻¹, respectively). Despite the relatively low Pmax, young leaves showed efficient low-light photosynthesis with a notable quantum yield (QY) of 0.0685 mol·mol⁻¹, trailing just behind mature leaves (0.0768 mol·mol⁻¹). During the mid-growth stage, mature leaves had the highest Pmax, followed by young and old leaves (16.38, 15.06, and 9.86 µmol CO₂·m⁻²·s⁻¹, respectively), with corresponding QY values of 0.0574, 0.0588, and 0.0365 mol·mol⁻¹, respectively. During the late growth stage, Pmax remained highest in the mature leaves, followed by young and old leaves (14.83, 13.43, and 6.80 µmol CO₂·m⁻²·s⁻¹, respectively), with corresponding QY values of 0.0574, 0.0588, and 0.0365, respectively. The results show that young leaves achieve efficient photosynthesis under low light, as indicated by their consistently high QY values across all stages, while old leaves exhibit reduced efficiency with both lower Pmax and QY. These results reveal that light use efficiency is highly dependent on both leaf and plant age, with the greatest senescence-associated decline occurring in old leaves at the late growth stage. Optimizing light use efficiency in strawberry plants, whether through light intensity control in indoor production or canopy management in open fields, must account for the leaf- and plant-age-dependent Pn–PAR relationship.
