Silicon uptake by plants typically discriminates against the light Si isotope, forming Si-enriched plants (δSi of 0–6‰). The reason for this relatively large isotopic fractionation remains unclear, mainly because the mechanisms of Si uptake by plants are yet to be understood. Silicon in plants can be found in the xylem, which is associated with exceptionally high δSi values. Phytoliths, microscopic structures of silica in plant tissues, have relatively lower δSi values. For example, it was reported that the mean δSi of phytoliths in various wheat organs were -1.4–2.1‰, which is lower than the typical range for vegetation (δSi of 0–6‰). Phytoliths are relatively soluble, and as plants decay they contribute to the terrestrial dissolved Si budget.