Aims Aluminium toxicity in acidic soils adversely affects wheat growth. Foliar-applied magnesium (Mg) contributes to mitigating soil acidity stress in wheat, but the mechanisms are unknown. This study explored the mechanism of foliar-Mg mediated enhancement of wheat growth in acidic soil. Methods Two contrasting near-isogenic wheat (Triticum aestivum L.) genotypes differing in Al resistance (Al-sensitive ES8 and Al-resistant ET8) were grown to the vegetative stage (Zadoks 24) in a reconstituted acidic soil (pH 0.1 M CaCl2 4.0) profile with three rates of foliar Mg (0, 200 and 500 mg Mg L − 1 using MgSO 4 .7H 2 O). Magnesium was applied to the foliage twice [14 and 28 days after sowing (DAS)], and plant growth and root exuded carboxylates were measured up to 42 DAS. Results Applying 200 mg Mg L − 1 to the foliage increased organic acid anion exudation from wheat roots by ~2-fold compared to 0 foliar Mg treated plants. The Al-resistant wheat genotype exuded 1.3-fold more ma-late and citrate from roots than the Al-sensitive genotype in the absence of foliar Mg. Malate exudation was delayed relative to citrate following foliar Mg application. The foliar-applied Mg increased shoot and root dry weight (by ~38 %), total root length (by ~33 %) and intrinsic water-use efficiency (by ~80 %) compared to plants treated with no Mg. Applying foliar Mg decreased soil acidity stress (as shown by a significant increase in chlorophyll fluorescence Fv/Fm ratio) in wheat compared to 0 foliar Mg. Conclusions Increased malate and citrate exudation is the underlying mechanism of enhanced wheat growth following foliar Mg application under acidic soil conditions.
