Rice cultivars ability to change nutrient solution pH in the presence of aluminum

Abstract

The objective of this work was to evaluate aluminum effect on the ability of two rice cultivars, Fernandes (tolerant) and Maravilha (sensitive), to change the pH of nutrient solutions with different NO₃^-/NH₄⁺ ratios. After plant exposure to 0 mM and 1.5 mM Al for 15 days, the amount of exudated protons, elongation, dry matter yield and Al content of roots and leaves were determined. Elongation and dry matter yield of roots and leaves reduced in the presence of Al independently of NO₃^-/NH₄⁺ ratio, and this reduction was intensified with increasing of NH₄⁺ concentration. Aluminum contents increased in roots and leaves with increasing of NH₄⁺ concentration in nutrient solution. An alkalization of the nutrient solution containing N exclusively in NO₃^- form was observed, but this alkalization decreased with Al treatment. In nutrient solutions containing NH₄⁺, on the contrary, an acidification was observed, which intensified with the increase of NH₄⁺ concentration. The tolerant cultivar always consumed more protons of the nutrient solution containing N exclusively in the NO₃^- form and less protons of that containing NH₄⁺, independently of the NO₃^-/NH₄⁺ ratio. This cultivar, therefore, showed higher ability to adjust its protons balance, changing the pH to values that favored lower Al uptake and higher tolerance to aluminum.