Chlorosis in Soybean as Related to Iron, Phosphorus, Bicarbonate, and Cytochrome Oxidase Activity

Abstract

PI-54619-5-1 (PI) and Hawkeye (HA) soybeans were grown using split-medium and split-root techniques to separate Fe from the precipitating effects of bicarbonate and P. For comparative purposes, these were grown in complete solution cultures where Fe, bicarbonate, and P were in direct contact with each other. PI and HA soybeans did not develop chlorosis when grown using split-medium or split-root techniques with roots in 10 meq/1 NaHCO3 at comparatively low P concentration. In comparison, PI soybeans developed chlorosis in complete solution cultures when 2 meq/1 NaHCO3 was in solution. Cytochrome oxidase activity decreased with increasing bicarbonate concentration in complete solution cultures, but was dependent upon P concentration in the split-root experiments. Bicarbonate in solution cultures increased the soluble P concentration in solution. Development of Fe chlorosis was more related to P concentration in solution or that absorbed by the plant than by bicarbonate concentration in solution. Cytochrome oxidase activity was affected by the P concentration. Bicarbonate does not appear to be a direct cause of Fe chlorosis or directly inactivate cytochrome oxidase. An effect of P concentration on cytochrome oxidase activity was observed.