Comparing stomatal characteristics and transpiration rates of greenhouse-cultivated tomato leaves according to their vertical positions

Accurate estimation of crop transpiration rate is crucial for optimizing water use efficiency and establishing effective irrigation strategies. However, transpiration rates vary depending on light interception differences between upper and bottom leaves within the plant canopy. This study aims to bridge the knowledge gap on how stomatal conductivity (g_s) varies with vertical leaf position within the whole canopy. Transpiration was measured using a load cell system, and a 10-minute interval measurement method was applied to minimize errors in transpiration rate estimation. During the experiment, the total accumulated transpiration per plant was 4.7 kg. The g_s varied by vertical leaf position, with mean contributions of 42.9% in upper leaves, 35.9% in middle leaves, and 21.6% in bottom leaves. Stomatal density was highest in upper leaves, followed by middle and bottom leaves, whereas stomatal length increased as density decreased (18.6, 24.7, and 27.7 μm, respectively). These results demonstrate the dominant role of upper leaves in canopy-level transpiration and indicate the need to consider vertical variation in stomatal characteristics when modeling transpiration. Reflecting these spatial differences may improve the accuracy of transpiration predictions and enhance water-use efficiency in controlled environments.