Ontogenetic gains in photosynthetic capacity and winter–summer photoprotective contrasts in wild Camellia formosensis across light environments

Abstract Camellia formosensis , Taiwan’s only native tea-producing tree, is near-threatened and increasingly cultivated as a forest-understory crop, yet light-management guidance derives largely from nursery seedlings. We measured gas exchange of mature wild trees growing in full sun or natural forest shade (10–20% relative light; three trees each) over an annual cycle, and chlorophyll fluorescence, relative chlorophyll content (SPAD) and the photochemical reflectance index (PRI) in winter and summer. Full-sun trees had a higher maximum net photosynthetic rate (Amax) than shaded trees in every season (summer: 14.2 vs. 9.0 µmol CO2 m-2 s-1), together with a higher light compensation point and dark respiration. Light-adapted photosystem II efficiency was markedly lower in winter than in summer in both light environments, coinciding with a site minimum temperature of 5.4 °C; non-photochemical quenching was higher under shade in winter but under full sun in summer. SPAD and PRI were consistently higher under shade. Wild-tree Amax (6.1–14.2 µmol CO2 m-2 s-1) was two- to three-fold that of one-year-old seedlings measured with the same protocol, consistent with an ontogenetic increase in photosynthetic capacity. Moderate shade conferred a pigment-based photoprotective signature shared across life stages, whereas winter chilling emerged as a field-specific constraint not captured by nursery trials.