Recovery of Corn Leaf Water Potential After Severe Water Stress

The re-establishment of vegetative growth after a period of water stress depends on the recovery of leaf water potential after rewatering. If the time to achieve recovery can be reduced, then overall plant production can be increased. This investigation examined the rates and patterns of leaf water potential recovery in corn plants (Zea mays L.) after alleviation of differing degrees of water stress. The experiments were done in a controlled environment chamber on corn plants grown in 5-liter pots of 1:3 mixture of silica sand:calcined clay. Leaf water potential was measured in situ with a thermocouple dewpoint hygrometer. Plants were stressed by withholding water and, immediately upon rewatering, the growth chamber lights were turned off and the recovery pattern in the dark was monitored. Leaf water potential of corn plants stressed to −10 to −11 bars recovered in the dark 40 to 50 min after rewatering. When the plants were stressed to water potentialvalues less than −11 bars they took between 95 and 300 min to recover. The recovery pattern always showed a distinct plateau phase during which time leaf water potential was relatively stable. The plateau occurred beween −9 and −7 bars and lasted 30 to 45 min. No plateau phase was observed in the rate of change of stalk diameter, but when stalks of severely stressed plants were severed under water to initiate recovery, we did not observe a plateau phase. Severing stalks under water, while leaf water potential was on a plateau, resuited in an immediate increase in potential. Applying pressure to the roots during the plateau phase caused af water potential to shift off the plateau. When pressure was released, however, the potential returned to the plateau and the plant continued a normal plateautype recovery. The results indicate that the main factors responsible for the plateau phase were in the roots, but that the stem and the leaves exerted some minor effects.