The vertical distribution of photosynthesis in crops of tobacco and sorghum.
Vertical distribution of photosynthesis in crops of tobacco and sorghum was determined at intervals throughout the day using a portable chamber exposing 5cm2 leaf to air containing 14CO2 for 30 sec. During all daylight hours photosynthesis declined with depth in the canopy. Stomata in lower leaves of a tobacco crop given adequate moisture failed to open even in bright light. While stomata of mid-canopy leaves opened, photosynthesis was slower than in upper leaves at equivalent stomatal conductances. Photosynthesis of upper leaves increased little at conductances between 0.6 and 0.9 cm/sec. Photosynthetic rates of sorghum were always greater than those of tobacco at equivalent stomatal apertures. Stomatal conductance and photosynthesis declined linearly with decreasing irradiance in all leaves of sorghum. RB.