Elevated root zone dissolved inorganic carbon can ameliorate aluminium toxicity in tomato seedlings.

•  The potential amelioration of Al (Al) toxicity by elevated dissolved inorganic carbon (DIC = CO2  + HCO3 - ) in the root medium was investigated in both NH4 + - and NO3 - -fed Lycopersicon esculentum (tomato) plants. •  Hydroponically grown L. esculentum seedlings were intermittently supplied with 50 µM AlCl3 and the nutrient solutions aerated with either 360 or 5000 ppm CO2 . Relative growth rate (RGR), nitrogen uptake, root respiration and root incorporation of DI14 C and subsequent partitioning were measured. •  Al reduced the RGR of plants grown with 360 ppm root-zone CO2 . At elevated root-zone CO2 , Al had no significant effect on the RGR of NO3 - -fed plants whereas the RGR of the NH4 + -fed plants was increased by 21%. Al decreased the respiratory quotient (Rq) by 15% at 360 ppm CO2 , but had no influence at 2000 ppm CO2 . Exudation of organic 14 C, especially of [14 C]-organic acids derived from root incorporation of DI14 C, was increased by Al. •  It is concluded that elevated DIC partially ameliorated Al toxicity by providing anaplerotic carbon for organic acid synthesis.