Anatomical variations along the leaf axis modulate photosynthetic responses of sorghum and maize under different water availabilities.

Water limitation leads to alterations in plants, including tolerance responses. Maize and sorghum are both C4 crops with contrasting drought tolerance, where several aspects of leaf anatomy and physiology are unclear. This work aimed to investigate the effect of drought on anatomical and photosynthetic traits along the leaf axis of maize and sorghum. Experiments were conducted in a greenhouse with maize and sorghum exposed to three irrigation conditions (field capacity (FC), 75% FC, and 50% FC). Three leaf regions (base, middle, and tip) were assessed for photosynthetic and anatomical parameters. Water limitation promoted reductions in maize leaves in terms of water-use efficiency, leaf thickness, xylem vessel diameter, and area of the bundle sheath; however, sorghum leaves increased these under the same conditions. The middle region of the leaf had higher values than other leaf parts for most parameters, while sorghum had increased ΦPSII, Fv/Fm, and ETR at the leaf base. Photochemical values increased in both species under water limitation. Maize had increased stomatal density compared to sorghum, which led to higher transpiration rates. Anatomical and photosynthetic traits varied along the leaf axis and were more reduced in maize than sorghum under drought. The middle region of the leaf was most responsive to these changes in both species.