INADEQUATE IRON SUPPLY AND HIGH BICARBONATE IMPAIR THE SYMBIOSIS OF PEANUTS (ARACHIS-HYPOGAEA L) WITH DIFFERENT BRADYRHIZOBIUM STRAINS

In the present study, we examined the effects of iron deficiency in an acid solution and in an alkaline solution containing bicarbonate on the growth and nodulation of peanuts inoculated with different bradyrhizobial strains or supplied with fertilizer nitrogen. Inadequate iron supply in acid solution decreased the number of nodule initials, nodule number and nodule mass. Alleviating the iron deficiency increased acetylene reduction but not bacteroid numbers in nodules. Nitrogen concentrations in shoots of inoculated plants increased as iron concentrations in solution increased when determined at day 30 but not at day 50. Higher iron concentrations in solution were required for maximum growth of plants reliant on symbiotic nitrogen fixation than for those receiving fertilizer nitrogen. Adding bicarbonate to the solution with 7.5-mu-M Fe markedly depressed nodule formation. This effect was much more severe than that of inadequate iron supply alone. Bicarbonate also decreased nitrogenase activity but did not decrease bacteroid concentrations in nodules. Both NC92 and TAL1000 nodulated peanuts poorly when bicarbonate was present. However, an interaction between iron concentrations in acid solutions and Bradyrhizobium strains on nodulation of peanuts was observed. Alleviating iron deficiency increased the number of nodule initials and nodules to a much greater extent for plants inoculated with TAL1000 than for plants inoculated with NC92.