Abstract:The effects of nitrogen types, HCO3- and HEPES on iron nutrition of pea genotypes, Sparkle and E107, were studied by solution culture under controlled conditions. Compared with NO3-N, NH4-N application resulted in earlier and significantly higher iron reducing activities, stronger utilization of apoplastic iron in roots, and more iron transported to shoot for both genotypes. The pH of solutions of Sparkle plants decreased more quickly when supplied NH4-N, however, there was no difference in solution pH in the two nitrogen types for E107. Apoplastic iron accumulated in roots was used up in low pH condition, but it could not be exploited by plants in 10mmol/L HCO3- buffering solution. However, plant roots in high pH condition were structurally and functionally undamaged, their iron reducing activities were higher than those grew in low pH solutions. The effect of HCO3- was similar with that of 5mmol/L HEPES. The results suggested that the effects of nitrogen types on iron nutrition were through changes of pH in rhizosphere and apoplast in plant, and the inhibition of iron nutrition of pea by HCO3- was not due to damage of root construction but the depression of iron reducing activity under high pH induced by HCO3-.