Bicarbonate Directly Induces Iron Chlorosis in Susceptible Soybean Cultivars1
- B. A. Coulombe,
- R. L. Chaney and
- W. J. Wiebold2
Four soybean [Glycine max (L.) Merr.] cultivars differing in susceptibility to iron (Fe) chlorosis in wet calcareous soils were grown in nutrient solutions to characterize the effects of phosphate (P) and bicarbonate (HCO-3) in inducing chlorosis. NaHCO3 (0 or 10 mM), P (10 or 400 µM as NaH2PO4, and NH+4 (0 or 300 µM) as (NH4)2SO4 were factorial treatments in a nutrient solution. Low Fe availability was maintained by supplying 5 µM Fe + 10 µM EDDHA, and excess CaCO3(pH 7.5). With no HCO-3 added, ‘T203’ (extremely chlorosis susceptible) was green at 10 µM P, but severely chlorotic at 400 µM P; ‘Wayne’ (chlorosis susceptible) was green at both P levels. Addition of HCO-3 caused chlorosis in T203 and Wayne at 10 or 400 µM P. Chlorosis resistant ‘AP9’ and ‘Hawkeye’ remained green with added P or HCO-3. Chlorosis ratings (1 = green to 5 = severely chlorotic) in the 0 HCO-3 + 10 µM P, 0 HCO-3 + 400 µM P and 10 HCO-3 + 400 µM P treatments, respectively, were: 1.0, 1.0, and 1.5 for AP9; 1.0, 1.0, and 1.4 for Hawkeye; 1.0, 1.2, and 3.9 for Wayne; and 1.0, 4.2, and 4.6 for T203. Low Fe concentrations in young leaves corresponded with high chlorosis ratings. Phosphorus concentration in young leaves did not change with HCO-3 at 10 µM P, but decreased with HCO-3 at 400 µM P. In the absence of HCO-3, Wayne was not chlorotic at either concentration of solution P, although this cultivar is known to be highly susceptible to chlorosis in the field. Bicarbonate-induced chlorosis in Wayne was not a result of increased solubility or plant uptake of P. Thus, HCO-3 was a direct factor in causing soybean chlorosis, and likely is also a cause in soils.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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