H⁺, Ca⁺⁺, and Mn⁺⁺ influence on sorghum seedling shoot growth

Plant response mechanisms for acid soil tolerance adaptability are generally unknown. Sorghum [Sorghum bicolor (L.) Moench] cultivars (Funk G522DR, GP 140, SC 599, TAM 428, SC 283, and SC 574) were grown in white quartz flintshot sand and watered with 0.01 M sodium acetate buffer at pH 4.0, 4.5, 5.0, 5.5, or 6.0 with concurrent treatments of Ca⁺⁺ (0, 10, 100 mgl^‐1 as CaCl₂) or Mn⁺⁺ (0, 1.4, 140.0 mgl^‐1 as MnCl₂). At the acid soil tolerance impact response phase (<10 days old), Ca⁺⁺ or Mn⁺⁺ did not influence seed germination (i.e., radicle exsertion). Ca⁺⁺ did not influence initial shoot growth. Increased H⁺ concentration greatly inhibited juvenile shoot growth equivalently in all six cultivars. This inhibition was explicable as an influence of gibberellic acid (GA) availability to the aleurone layer and was explained as an accumulation (partitioning) of GA into lipid cellular constituents. Excess Mn⁺⁺ further exacerbates this condition by limiting GA biosynthesis.