Silicon Mitigates Aluminum Toxicity of Tartary Buckwheat by Regulating Antioxidant Systems

Aluminum (Al) toxicity is a considerable factor limiting crop yield and biomass in acidic soil. Tartary buckwheat growing in acidic soil may suffer from Al poisoning. Here, we investigated the influence of Al stress on the growth of tartary buckwheat seedling roots, and the alleviation of Al stress by silicon (Si), as has been demonstrated in many crops. Under Al stress, root growth (total root length, primary root length, root tips, root surface area, and root volume) was significantly inhibited, and Al and malondialdehyde (MDA) accumulated in the root tips. At the same time, catalase (CAT) and ascorbate peroxidase activities, polyphenols, flavonoids, and 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) free-radical scavenging ability were significantly decreased. After the application of Si, root growth, Al accumulation, and oxidative damage were improved. Compared to Al-treated seedlings, the contents of ·O₂⁻ and MDA decreased by 29.39% and 25.22%, respectively. This was associated with Si-induced increases in peroxidase and CAT enzyme activity, flavonoid compounds, and free-radical scavenging (DPPH and ABTS). The application of Si therefore has positive effects on Al toxicity in tartary buckwheat roots by reducing Al accumulation in the roots and maintaining oxidation homeostasis.