INFLUENCE OF INCREASING BICARBONATE CONCENTRATIONS ON PLANT-GROWTH, ORGANIC-ACID ACCUMULATION IN ROOTS AND IRON UPTAKE BY BARLEY, SORGHUM, AND MAIZE

Barley, sorghum, and maize plants were grown in nutrient culture with increasing concentrations of bicarbonate supplied as NaHCO3 (0-20 mM) and harvested at 0, 2, 4, and 8 days of treatment. Bicarbonate induced symptoms of iron (Fe) deficiency (chlorosis) in all three plant speci es, but sorghum and maize were more sensitive than barley. Increases i n the concentration of HCO3-ions in the nutrient medium markedly decre ased dry weight of roots and shoots in all three crop species. These e ffects became more distinct with time, particularly at 10 and 20 mM of bicarbonate supply. In contrast to root dry weight, however, root len gth was depressed by bicarbonate to a lesser extent in barley than in sorghum and maize. In all three species bicarbonate supply resulted in an accumulation of organic acids in roots and a decline in uptake and translocation of Fe. In addition, inhibition of root growth by bicarb onate was associated with enhanced net efflux of K+ and NO3-indicating an adverse effect of bicarbonate on root plasma membrane integrity as a primary cause of root growth inhibition. Impairment of Fe acquisiti on may be predicted as a consequence of the root growth inhibition.