Silicon in Developing Nuts of the Sedge Schoenus nigricans

The accumulation of silicon in the nutlets of Schoenus nigricans, a sedge from wet dune slacks, was studied during nutlet development from ovule fertilization up to nutlet ripeness in plants from a submediterranean (Eastern Italy) and a temperate (North Holland) population at their natural sites. There was a rapid increase of the Si concentration between 4 and 10 weeks after fertilization of the ovules at the first position, but a delayed increase at higher spikelet position. Whereas the Si content of the surrounding tissues, i.e. shoot, bracts, and spikelet axis, remained below 3%, Si concentration in the pericarp of the nutlets at the first and second spikelet positions increased during nutlet development up to 34% Si. Nutlets at higher spikelet positions, having a shorter development time, contained significantly less silicon. Differences in the climate did not affect the Si concentration. Plants grown in desiccated dune slacks had a low silicification of the nutlets. Within the pericarp there was a strong Si gradient from inward to outward, accompanied by a similar trend of Ca, K and Cl, indicating a passive transport with the transpiration stream; the rapid increase of the Si concentration during pericarp development, however, made it necessary that a preferential and thus active Si transport to the pericarp was involved. The chemical Si-form in the pericarp was mostly biogenic opal, but correlation with the hydrogen concentration did not exclude the formation of Al silicates. The ecological consequences of pericarp silicification are shortly discussed. © 1995, Gustav Fischer Verlag, Stuttgart. All rights reserved.