Effects of aluminium on the root activity, organic acids and free proline accumulation of alfalfa grown in nutrient solution

The effects of elevated aluminium (Al) concentrations on parameters indicating Al toxicity and Al detoxification were evaluated in two alfalfa populations from different acidic soil environment. Plants were grown in nutrient solutions at pH 4.5, 5.5 and 6.0, with different levels of Al contamination for 30 days. Shoot heights and root activity were significantly decreased in the Al treatment while free proline concentration was significantly increased. Furthermore, citric acid and oxalic acid concentrations tend to increase with increasing Al concentration. Different responses were also observed between the two populations. Shoot height, free proline concentration and root activity were significantly higher for alfalfa plants collected from an acidic soil environment. These plants also exhibited higher concentrations of citric and oxalic acids when exposed to 100 mu M Al at pH 4.5. Overall, the results indicate that alfalfa plants grown on acidic soils might develop mechanisms to be less affected by high Al concentration.