The effect of soil compaction on wheat during early tillering: II. Concentrations of cell constituents

Wheat (Triticum aestivum L. ev. Eradu) was grown in the field on a deep loamy sand which had either a compact soil layer (compact soil) between 10 and 55 cm depth or a deep‐tilled profile (loosened soil). Concentrations of metabolites were affected by the presence of mechanical impedance. The concentrations of soluble sugars (including glucose, fructose and sucrose), free amino acids and inorganic ions (K⁺, Na⁺, NH₄ ⁺, Cl⁻, NO₃ ⁻, H₂PO₄ ⁻, SO₄ ²⁻) in consecutive 1 cm root segments of the seminal roots are reported. When tissues equidistant from the apex were compared, the concentrations of free amino acids were greater in roots from loosened soil; soluble sugars were also more concentrated in roots from loosened soil except in the apical 1 cm of the root. However, comparing root tissues of the same age (calculated from elongation rates), showed that concentrations of soluble sugars were smaller in roots from loosened soil. Potassium, Na⁺, Cr and SO₄ ² were present in fairly constant concentrations along the terminal 4 cm of the root; NO₃ ⁻ and H₂PO₄ showed more distinct gradients along the axis. Roots from loosened soil had higher NO₃ and lower SO₄ ²⁻ concentrations than those from compact soil. The total concentration of solutes assayed was 19–31 % smaller in roots growing in compact soil than in roots from loosened soil. Soluble sugar concentrations in shoots as a whole were 21 % greater in plants taken from compact soil than those from loosened soil, suggesting that the lower shoot growth rates of the former were not the result of carbohydrate shortage.