Stomatal closure of maize hybrids in response to drying soil

In studying differences among genotypes in physiological response to drying soil, it is important that the genotypes be compared at equivalent soil water contents. Unless the comparisons are made at the same soil water content, genotypic difference may only be a consequence of differences in soil water status. In this study, the objective was to compare stomatal closure among eight maize (Zea mays L.) hybrids in response to soil drying. Three greenhouse experiments were conducted in which daily transpiration and soil water content were measured by weighing each pot. Daily transpiration of stressed plants was normalized relative to that of control plants to minimize variation due to environmental effects. This daily transpiration ratio also was normalized relative to the well-watered condition to minimize variation among plants and was recorded as normalized transpiration ratio (NTR). Dairy soil water content was expressed as the fraction of transpirable soil water (FTSW). Among the eight hybrids examined, there were statistical differences in the FTSW at which the stomata began to close. In all experiments, Hybrid 3165 was consistently among the hybrids that began to close their stomata at small FTSW values; whereas, Hybrid 3737 began to close its stomata at large FTSW values. While we surveyed a small genetic base, our results indicated genotypic differences exist for stomatal responses to a drying soil.