ALLEVIATION OF WATERLOGGING DAMAGE TO YOUNG BARLEY PLANTS BY APPLICATION OF NITRATE AND A SYNTHETIC CYTOKININ, AND COMPARISON BETWEEN THE EFFECTS OF WATERLOGGING, NITROGEN DEFICIENCY AND ROOT EXCISION

A study was made of the effects of either 6‐benzylaminopuiine (BAP), a synthetic cytokinin, or calcium nitrate on the response of the shoots of 13‐day‐old barley plants to soil waterlogging. Spraying leaves daily with BAP resulted in small improvements in leaf extension and retarded the premature loss of chlorophyll in the older leaves after 7 days waterlogging, but the rates of accumulation of dry matter and inorganic nutrients in shoots were reduced to the same extent as in unsprayed plants. After a further 7 days waterlogging, during which spraying was discontinued, plants treated with BAP were no longer appreciably different from untreated ones. When calcium nitrate was added daily to the surface of the waterlogged soil, no symptoms of waterlogging damage appeared. Leaf extension, shoot weight, emergence of tillers, chlorophyll concentrations and the accumulation of inorganic nutrients in shoots were similar to those in plants in non‐waterlogged soil after 7 and 14 days. The effect was dependent on the presence of a narrow zone of aerated soil close to the surface, in which root growth and function could continue. When plants were grown for 13 days in aerated nutrient solution, and then transferred to solutions lacking nitrate, the development of leaf chlorosis, the decrease in the concentration of nitrogen in the shoots and their retarded accumulation of dry matter were all similar to that caused by waterlogging. The premature loss of chlorophyll in the older leaves was retarded by spraying with BAP. Chlorosis of the older leaves could also be promoted in plants in aerated nutrient solution by excising part of the root system. Mechanisms by which BAP and calcium nitrate alleviate symptoms of waterlogging damage, and the significance of nitrogen deficiency and root excision in relation to waterlogging damage, are discussed. Copyright © 1979, Wiley Blackwell. All rights reserved