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 species, but sorghum and maize were more sensitive than barley. Increases in the concentration of HCO3-ions in the nutrient medium markedly decreased dry weight of roots and shoots in all three crop species. These effects became more distinct with time, particularly at 10 and 20 mM of bicarbonate supply. In contrast to root dry weight, however, root length 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 bicarbonate 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 acquisition may be predicted as a consequence of the root growth inhibition.