Temporal water use by two maize lines differing in leaf osmotic potential

Two lines of maize which had different levels of expressions of leaf osmotic potential (OP) under water-deficit conditions in the field were previously found to differ in leaf area duration and water extraction at soil depths greater than 0.80 m. In the current study, the hypothesis was explored that the difference in leaf OP between the two lines was associated with differences in transpiration rate which in turn had a major effect on the temporal dynamics of soil water use. The line with the lowest (most negative) OP in the early stages of the soil drying cycle was found to have the greatest transpiration rate and delayed wilting which was consistent with the original field observations. However, with further soil drying, the line with higher OP was able to sustain transpiration over a longer time period and actually reached the end point of transpirable soil water at a later date. The results of these experiments highlighted the necessity of accounting for temporal dynamics when interpreting crop water use in response to soil drying, particularly when comparing genotypes with differing OP.