Chapter 1 Silicon in plants: Facts vs. concepts

The facts of silicon (Si) in plant life are one thing; the concepts regarding Si in plant physiology are another thing altogether. Most terrestrial plants grow in media dominated by silicates, and the soil solution bathing roots contains Si at concentrations exceeding those of phosphorus (P) by roughly a factor of 100. Plants absorb the element, and their Si content is of the same order of magnitude as that of the macronutrient elements. The general plant physiological literature, however, is nearly devoid of Si. The reason for this marked discrepancy is the conclusion that Si is not an “essential” element because most plants can grow in nutrient solutions lacking Si in their formulation. Such Si-deprived plants are, however, experimental artifacts. They may differ from Si-replete plants in (i) chemical composition; (ii) structural features; (iii) mechanical strength; (iv) various aspects of growth, including yield; (v) enzyme activities; (vi) surface characteristics; (vii) disease resistance; (viii) pest resistance; (ix) metal toxicity resistance; (x) salt tolerance; (xi) water relations; (xii) cold hardiness; and probably additional features. The gap between plant physiological facts and plant physiological concepts must be closed. The facts of Si in plant life will not change; hence it is the concepts regarding the element that need revising.