Effects of aluminium on nodulation and early growth of four tropical pasture legumes

Abstract

Effects of aluminium concentrations of 0, 12.5, 25, 50, 100 or 125 ¦M on the nodulation and growth of Centrosema pubescens cv. Belalto, Macroptilium lathyroides cv. Murray, Stylosanthes guianensis cv. Schofield and Stylosanthes guianensis cv. Oxley were studied in solution cultures maintained at pH 4.5. The strains of Rhizobium used were CB1923, CB756, CB756 and CB1650 respectively. Solutions containing >25 ¦M aluminium (Al) delayed the appearance of nodules and reduced the percentage of plants which nodulated and the number and dry weight of nodules produced by all four legumes. At 125 ¦M Al, the proportion of plants which nodulated ranked in the order M. lathyroides (42%) > C. pubescens (29%) > Schofield stylo (16%) > Oxley stylo (0%). However, there were no significant effects of Al on dry matter production in M. lathyroides or C. pubescens. In Schofield stylo 250 ¦M A1 caused a small but significant yield reduction. In Oxley stylo, the yield reduction was significant at 25 ¦M , but became large only at 125 ¦M. It is concluded that in M. lathyroides, C. pubescens, and possibly Schofield stylo, nodulation is more sensitive to aluminium toxicity than is host plant growth. In Oxley stylo, threshold concentrations were similar for significant effects of aluminium toxicity on nodulation and growth.