Earthworms can increase mobility and bioavailability of silicon in soil

• Earthworms increase concentrations of water-extractable Si in soil.
• Earthworms increase concentrations of Si(OH)4 in soil.
• Increased soil Si availability due to earthworms occurs in soils with different texture.
• Increased soil Si availability due to earthworms occurs in soils with different CaCO3 content.
• Earthworms increase Si movement via xylem of plants.

Earthworms are one of the dominant groups of soil macro-invertebrates in many terrestrial ecosystems affecting nutrient cycling and plant growth. However, it is not well known how earthworms can influence availability of silicon (Si) as an element whose beneficial role in agricultural systems has been widely recognized. The objectives of this study were: (1) to determine the effect of earthworms on the mobility of Si in soil, and (2) to determine whether earthworm induced effects on Si mobility are of importance for the availability of Si to plants (Cucumis sativus L. and Zea mays L.). Two soils (a sandy loam soil and a sandy soil) with two levels of two independent treatments (±CaCO3 and ± earthworms) were used. Concentrations of water-extractable Si and monosilicic acid (Si(OH)4) in casts/soils and Si movement via xylem of plants were measured. Casts of earthworms – endogeic Aporrectodea caliginosa (Savigny) and anecic Lumbricus terrestris L., had generally higher amounts of water-extractable Si (by 2.0–12.0 times) and Si(OH)4 (by 1.3–3.5 times) compared with bulk soils, irrespective of soil type and application of CaCO3. Bioturbation of the sandy loam soil by living earthworms were generally of major importance in improving xylem translocation of Si from roots to shoots in cucumber and maize. The results highlight for the first time the importance of earthworms in plant acquisition of Si and biogeochemistry of Si.