Silicon alleviates mercury toxicity in garlic plants

Silicon (Si) can increase plant stress tolerance. Mercury (Hg) is one of the major elements of heavy metal pollution. However, little attention has been paid to the possible effect of Si on Hg toxicity in plants. Here, the effects of Si on growth, photosynthesis, Hg accumulation and antioxidant defense were investigated in garlic grown in pots under Hg stress. Before sowing, Hg and Si were added at 3 mg Kg−1 and 500 mg Kg−1, respectively. The treatments included CT (control), Si, Hg and Hg + Si. The results showed that in non-stress conditions, added Si did not affect the garlic growth, photosynthetic gas exchange, malonaldehyde concentration or activities of antioxidant enzymes in leaves, except that it increased the superoxide dismutase activity. Under Hg stress, the garlic growth, leaf net photosynthetic rate, stomatal conductance, transpirational rate and superoxide dismutase activity in leaves were all inhibited, while the malondialdehyde concentration was increased; whereas these changes were all reversed in the presence of added Si. Added Si significantly decreased Hg concentrations in the root, bulb and shoot, and it also decreased exchangeable Hg level in the soil. These results suggest that Si could alleviate Hg toxicity in garlic through improving antioxidant defense ability, and decreasing Hg availability in soil and thus Hg uptake.