Effects of aluminum on nutrient solution pH and nitrate/ammonium uptake by triticale

Aluminum (Al) plant tolerance has been frequently associated with a pH increase in the rhizosphere. The changes in pH are dependent on plant genotypes and ionic composition and strength of nutrient solutions. This work was performed in order to study in triticale (Triticosecale Wittm.) the association of pH change with nitrogen (N) uptake and growth performance in acid conditions. Three-day-old seedlings were treated with Al (185 mu M) in solutions having different proportion nitrate/ammonium (NO3/NH4), 15/1 and 8/1, but the same total N content. Along the period with Al treatment, several measurements have been made: pH, every day; NO3 and NH4 uptake from the solution as well as shoot and root biomass production every two days (five and seven days of plant age). The maximum growth inhibition (30%) of fresh weight was found in roots of plants in the 15/1 (NO3/NH4) nutrient solution. The presence of a higher proportion of NH4 (8/1 solution) had a protective effect on Al damage as shown by less growth inhibition and less reduction in NO3 uptake. Changes in pH apparently were not relevant for the tolerance. The results suggest that NH4 fertilization may be useful for alleviating Al toxicity in triticale.