Canopy position influences cultivar differences in leaf gas ex-change in apple trees across contrasting growing seasons

The dataset that supports the following paper: Canopy light environment creates contrasting microclimatic conditions that influence leaf physiological acclimation within fruit tree canopies. However, whether cultivar differences in leaf gas exchange are expressed similarly across canopy positions remains unclear. This study evaluated the influence of canopy position on leaf gas exchange in two commercial apple (Malus domestica) cultivars, “Golden” and “Braeburn”, under well-irrigated conditions during two climatically contrasting growing seasons. Stomatal conductance (gs) and transpiration (E) were monitored on sun-exposed and shaded leaves, while photosynthetic light-response curves characterized their physiological acclimation. The two seasons differed markedly in atmospheric evaporative demand, while soil water availability remained non-limiting. In both cultivars, sun-exposed leaves showed higher maximum photosynthesis, light saturation points, gs, and E than shaded leaves, confirming acclimation to higher irradiance. However, cultivar differences depended on canopy position. Under high irradiance, Golden exhibited greater photosynthetic capacity than Braeburn, whereas under shaded conditions Braeburn maintained higher photosynthetic rates. Seasonal atmospheric conditions further influenced these differences, which were more pronounced under higher vapor pressure deficit. Overall, canopy position modulated cultivar differences in leaf gas exchange, highlighting the importance of considering leaf position when assessing physiological responses and comparing apple cultivars under contrasting climatic conditions.