Growth and N2 fixation response of arrowleaf clover to manganese and pH in solution culture

Abstract

Arrowleaf clover (Trifolium vesiculosum L. Savi) is grown in the southern USA where soil acidity and associated toxic ions may reduce growth and N2 fixation. Limited information is available on acid tolerance of this important winter annual forage. Two solution culture experiments were conducted to evaluate the growth and N2 fixation sensitivity of arrowleaf clover to Mn and acidity. In the first experiment, the N2 fixation activity of three strains of Rhizobium leguminosarum bv trifolii decreased when plants were grown with 250 or 500 μM Mn. The most effective strain was more tolerant of 250 μM Mn than the other two strains. Very little N2 fixation or plant growth occurred for plants at the higher Mn concentration. In the second experiment, half of the plants received 14 mg N pot−1 each week to supplement N2 fixation in addition to Mn (0, 250, and 500 μM) and pH (4.5, 5.5, and 6.5) treatments. pH influenced plant growth only when no additional N or Mn was present. Dry matter yield was 30% lower at pH 4.5 than at pH 6.5. Mineral N more than doubled plant growth and increased N2 fixation 35 to 80% in the absence of Mn. In the presence of Mn, growth and total N were greater for plants receiving mineral N but Mn inhibited growth and N2 fixation of both groups of plants. Arrowleaf clover was moderately tolerant of Mn. The two experiments indicate that the response of arrowleaf clover to Mn is dependent on the N status of the plants and that pH had a minimal affect on its growth.