Uptake of silica by grapevines from soil and recirculating nutrient solutions

Abstract

The uptake of silica by grapevines was investigated both in the field and in hydroponic cultures. In aqueous soil suspensions (14 d at 20 °C) of 6 different locations (clay/loam) an equilibrium of 55-71 ppm of soluble silica (expressed as SiO₂) was measured; the content of grapevine leaves at harvest time was between 0.44 and 0.73 % of the dry matter, the concentrations being correlated with the silica solubility of the relative soil. Before budburst xylem exudates contained only about 1-4 ppm SiO₂ (rising with soil temperature), whereas during summer up to 68 ppm were measured.
Six different grapevine cultivars were grown in recirculating nutrient solutions supplied with different amounts (112, 10 and 0 ppm) of SiO₂; the solutions were changed weekly. The average SiO₂ content of leaf dry matter at harvest time (0.1-2 %) was correlated with leaf age and the SiO₂ concentration of the nutrient solution whereas in stems and petioles it was always less than 0.1 %. Significant varietal differences could be found only for cv. Regent which accumulated about 20 % more SiO₂ than the other varieties from the 112 ppm solutions. By the end of the vegetation period fresh leaves from plants grown on 112 ppm contained always around 0.1 % of water soluble SiO₂, irrespective of the leaves' age whereas the total amount of SiO₂ was up to 2 % in old leaves from the basis of the shoots and less than 0.5 % in the apical region. In the leaf center the silica concentration was always around 50 % lower than in the leaf periphery.