Influence of Sulfate Concentration in Mineral Solution on Ryegrass Grown at Different pH and Aluminum Levels

Abstract

The objective of this study was to clarify the effects of sulfate and phosphate at different sulfate concentrations, pH levels, and aluminum (Al) concentrations on aluminum phytotoxicity in ryegrass grown in mineral solution. The results demonstrated that, in general, both a high sulfate concentration and phosphate in the mineral solution had a positive effect on the detoxification of Al. Increased sulfate concentrations did not have a clear effect on the sulfur (S) or phosphorus (P) content within the shoot or root, because their uptake is regulated by Al uptake in the ryegrass, but a very good relationship was found between the P root content and Al root content (r = 0.944**; p ≤ 0.01). The P and S root content and the aluminum:phosphorus molar ratio in roots were negatively correlated to shoot dry weight (r = −0.747**, −0.619** and −0.816**, respectively; p ≤ 0.01), suggesting that Al tolerance is related to P nutrition. Relative root dry weight (RTI) measured at 90 d was a more sensitive indicator of Al toxicity than relative root or shoot length (RRL, RSL). This study showed that the most important Al detoxifying mechanisms in the ryegrass were apparently physiological Al-PO4 precipitation inside the root and chemical AlSO4 + complex formation in the nutritive solution.