Effect of bicarbonate on iron reduction by soybean roots¹

Published as Paper no. 8801 in the Journal Series of the Nebraska Agric. Exp. Stn. Research funded in part by the Nebraska Soybean Development, Utilization and Marketing Board.

Abstract

Release of reducing compounds by soybean (Glycine max (L.) Merr.] roots has been identified as an adaptive response mechanism to iron‐deficiency conditions which result in chlorosis. These compounds facilitate the conversion of Fe⁺³ to the metabolically active Fe⁺² form, allowing for increased uptake by roots in solution culture experiments. Degree of chlorosis is closely associated with HCO₃ concentration; however, the relationship between that ion and root reduction potential apparently has not been studied. We examined the effect of HCO₃‐ on root reduction potential of ten commercially‐grown soybean cultivars known to differ in chlorosis expression in the field. Root reduction potential was measured spectrophotometrically at 594 nm on samples of nutrient solution containing reduced Fe⁺² . Plants were grown with 5 mM NaHCO₃ or in HCO₃ ^‐‐free solutions. Averaged over cultivars, 0.205 umoles Fe⁺³ were reduced in the HCO₃ ^‐‐free solutions while only 0.009 umoles Fe⁺³ were reduced in the solutions containing HCO₃ ^‐. No significant differences were observed among cultivars for root reduction potential within either HCO₃ ^‐ treatment. Results from this study suggest that HCO₃ ^‐ may inhibit iron absorption by limiting the ability of roots to release reducing compounds which make available Fe⁺2 in the soil solution. This may partially explain the role of HCO₃ ^‐ in reducing chlorosis.

Notes

Published as Paper no. 8801 in the Journal Series of the Nebraska Agric. Exp. Stn. Research funded in part by the Nebraska Soybean Development, Utilization and Marketing Board.