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.

Keywords:

• ryegrass sulfur content
• ryegrass phosphorus content
• aluminum toxicity
• Lolium multiflorum
• nutritive solution
• sulfate

ACKNOWLEDGMENTS

The authors would like to thank the National Research Council of Chile (Fondecyt N° 1990–873 grant), the Education Ministery (MECESUP FRO039), and the Andes National Foundation C-17355-28 grants for financial support and Olivia Haesloop (biology undergraduate, Yale University) for help with the English language.

Notes

*is significant at < 0.05;

**is significant at < 0.01, and ns is nonsignificant.

¹Dry wt. of roots grown with Al/dry wt. of roots grown without Al ×100.

²Shoot length of ryegrass grown with Al/shoot length of ryegrass grown without Al ×100.

³Root length of ryegrass grown with Al/root length of ryegrass grown without Al ×100.