Effects of excess aluminium and manganese on growth and phosphorus nutrition of mycorrhizal sorghum grown under acidic conditions

Abstract

Soil acidity is often associated with excess Al and Mn and these conditions usually reduce plant growth and inhibit P uptake. A major effect of vesicular-arbuscular mycorrhizal (YAM) fungi is to enhance P uptake in plants. This study was conducted to evaluate the effects of excess Al and Mn on growth and P nutrition of Sorghum bicolor ( (L.) Moench) colonised by two isolates of VAM (Glomus etunicatum UT316 and Glomus intraradices UT143) under acidic conditions. Plants were grown with and without VAM in hydroponic sand culture irrigated with nutrient solution (pH 4.8) containing 0, 35, 70 and 105 µM Al (as Al K(SO4)2) and 0, 270, 540 and 1080 µM Mn (as MnCl2) above the initial 18 µM in the basal nutrient solution. Percent root colonisation by VAM increased as Al in solution increased and decreased as Mn in solution increased. VAM ameliorated Al and Mn toxicities, even though Mn toxicity symptoms were more pronounced in VAM than in non-VAM plants. UT316 was more effective in alleviating plant dry matter yield (DMY) reductions caused by excess Al or Mn than UT143 and excess Al or Mn effects appeared to be related to the particular VAM isolate colonising roots. Toxicity symptoms of plants grown with excess Al appeared to be associated with P nutrition, but not for plants grown with excess Mn.