TOLERANCE OF LESPEDEZA BRADYRHIZOBIUM TO ACIDITY, ALUMINUM, AND MANGANESE IN CULTURE MEDIA CONTAINING GLUTAMATE OR AMMONIUM

Lespedeza juncea (sericea lespedeza) is a perennial forb-legume often planted on acid disturbed lands to fix N2. The abilities of 14 lespede za Bradyrhizobium strains (cowpea classification group) to grow in a d efined medium (glutamate as the N source) were determined at different pH values with varied amounts of Al and Mn. Growth response times wer e determined based on days required for strains to achieve a detectabl e amount of turbidity. Growth was not significantly affected at pH 4.5 or by 500 muM Mn compared to pH 6.7. Addition of 50 muM Al at pH 4.5 significantly (P less-than-or-equal-to 0.05) decreased growth of half of the strains in comparison to controls at pH 4.5. A pH of 4.3 signif icantly (P less-than-or-equal-to 0.05) decreased growth of 93% of the strains. Addition of 50 and 80 muM Al at pH 4.3 significantly decrease d growth of most strains compared to pH 4.3 controls. Most strains did not become turbid at pH 4.1, the most inhibitory treatment. Based on growth response times, bacterial growth may be sufficient in soils at or above pH 4.5 to insure adequate nodulation. Strains isolated from a cid disturbed lands were generally more tolerant of inhibitory treatme nts than other strains, including commercial strains. Plate count expe riments indicated that differences in growth response times were the r esult of sustained decreased growth rates although initial lag time pe riods for biological adjustment also occurred. These results agreed wi th those obtained by a new method using a less pH-buffered growth medi um (ammonium as the N source) in which the bacteria decreased the pH a s they multiplied, theoretically to a stable inhibitory value (i.e. to lerance value).