Contrasting responses to soil and water salinity in stomata and canopy traits produced convergence of water-use in tomatoes (Solanum esculentum) and okra (Abelmoschus esculentus): Application to water management

BACKGROUND: Salinity constrains agricultural sustainability and crops differ in their response. We tested the hypothesis that contrasting responses in canopy and stomatal traits to salinity will cause convergence of water-use in okra and tomato.
RESULTS: Stomata were found almost exclusively (>90%) on the lower leaf surface of tomato, but okra produced ~30% of stomata on the upper leaf surface. While salinity reduced the magnitudes of canopy and stomata traits in tomato, stomata traits were either unaffected or enhanced in okra. Salinity reduced the rates and duration of stomatal conductance (gs) in both crops, more severely in tomato, in which gs was restricted to early mornings in contrast to its bell-shape trend in okra. The superiority of okra in its stomata traits was compensated by the larger plant canopies in tomato, resulting in both daytime canopy transpiration and total plant water-use within 17% and 28%, respectively, of each other for the two crops. A tight stomatal control of transpiration that minimised use of water and its uptake from the soil conferred a superior salinity tolerance on tomato over okra. In both crops, stomata density (D) was inversely correlated with stomata area (A), while water-use was positively correlated with plant leaf area, in addition to D and A in tomato; gs was also correlated with stomata area index in tomato.
CONCLUSION: Differences in water-use for both crops were relatively narrow, despite the several-fold differences in their canopy and stomata traits. Under saline conditions, irrigation intervals should be long for tomato but short for okra.