Uptake of Monosilicic Acid by Trifolium Incarnatum (L.)

Abstract

Silica is present in soil and culture solutions as undissociated monosilicic acid (H4Si04) and this suggests that its uptake by plants would be a passive, non-selective process. We have earlier reported (Jones and Handreck 1965) that the overall uptake by oats (Avena sterilis cv. Algerian) can be accounted for simply in terms of the concentration of monosilicic acid in the soil solution and the amount of water transpired. Thus, when grown in two potted soils containing 7 and 67 p.p.m. Si02 in solution, oat plants at maturity contained 28 and 274 mg Si02 per plant respectively, having transpired 3·9 litres of water and produced 7·0 g of dry matter. The concentration of silica in xylem sap from oats is similar to that in the external solution. When Trifolium incarnatum (L.) (crimson clover) was grown in these two soils the plants had transpiration ratios of 510-530 but contained silica in concentrations which were only 5-10% of those in oats. This suggests that T. incarnatum has some means of excluding silica from the tops; we have examined this further by measuring the concentration of silica in the xylem sap.