Aspects of Adaptation by Wheat and Barley to Soil Moisture Deficits

Abstract

Experiments were designed to examine whether drought imposed on plants between sowing and flowering endows them with adaptations which enable them to cope more effectively with drought occurring during grain growth. Specifically, the character sought was adaptation persistence.

In two experiments, one in a growth chamber, the other in a glasshouse, plants of two-rowed and six-rowed barleys, and of durum and aestivum wheats, were grown in canopies in 1-metre-deep pots filled with soil, so that the development of water stress might approximate that in the field. Various drying cycles were imposed during the vegetative phase, after which plants were rewatered and allowed to fill their grain during a further drying cycle.

During the initial drying cycles there were morphological changes, including changes in area per leaf, leaf area per plant, specific leaf weight and in the numbers of plant organs; the plants to which water was applied sparingly had better water-use efficiency than those with a plentiful supply. On rewatering, however, the previously droughted plants became prodigal in their water use and in the final drying cycle there was little evidence that the earlier responses improved the efficiency of water use either per unit dry matter gain or per unit grain produced. Thus any adaptations were not persistent. Indeed, in general, plants which were heavier at anthesis (i.e. those which had lost more water by this stage), used water most efficiently in grain production. This result is discussed in relation to current photosynthesis and the remobilization of reserves during grain-filling. ¹⁴C data indicated that barley plants exposed to drought during grain growth did not retranslocate more stored materials than those which were frequently watered during this stage.