Fig. 4 Water potential gradients from substrate or hydroponic nutrient solution to roots and then leaves measured in the light (left) and water status of flag leaves in the light and dark (right). Dark measurements were made 4 h after lights had been turned off. Closed symbols represent hydroponic culture; open symbols represent zeoponic substrate with microporous tube irrigation culture (ZPT). Symbols represent means; error bars indicate SD, where larger than symbol size. Substrate and root water potentials, and nutrient solution osmotic potential, n = 3; leaf water potential, n = 6