5.4 ǀ Silicon
Low Si levels are also a feature of highly-weathered acid soils.
Although a ‘beneficial’ rather than an essential nutrient, it is taken
up in large amounts by rice plants, and applications to rice under Fe
toxic conditions have been found to reduce Fe uptake and produce fewer
leaf symptoms (Becker, Ngo & Schenk, 2020; dos Santos et al., 2020;
Dufey, Gheysens, Ingabire, Lutts & Bertin, 2014). Its specific role in
plant metabolism is not well understood, but probably involves a
stabilising effect on cell walls as an inert deposition in lignified
cells and also by modulating lignin biosynthesis (Broadley et al.,
2012). Becker et al. (2020) found decreased Fe2+uptake on addition of Si to nutrient culture, which they attributed to
enhanced formation of the root exodermal Casparian strip. Chalmardi,
Abdolzadeh & Sadeghipour (2014) found Si application improved
antioxidant enzyme activity under Fe toxic conditions.