FIGURE 1.

Overview of the Si cycle between soil, plants, and its subsequent intake by humans. (a) Classes of Si compounds in soil, modified with permission from Sauer et al. (2006). Weathering of silicate-containing minerals releases Si as silicic acid into soil solution, which is passively or actively taken up by plant roots (cf. Figure 2, active uptake and transport mechanisms). Presence of Si both in soil (b) and plants (c) protects plants against biotic and abiotic stresses. (d) Dietary Si sources for human intake, with maximum contribution from plant-based food products as represented by arrow thickness (see also Table 1). Broken line indicates very low level of contribution. In (e) nutritional benefits of Si for human health are listed. See main text for more details.