The relationship between silicon availability, and growth and silicon concentration of the salt marsh halophyte Spartina anglica

Analysis of silicon concentrations of various halophytes from salt marshes in the S.W. Netherlands shows that the silicon concentration of Spartina an glica (Gramineae) is relatively high. To study the influence of dissolved S i concentrations on growth and plant tissue concentrations of S. anglica, s ilicic acid was introduced into the sediment of natural patches of this hal ophyte occurring on a tidal flat. This resulted in a strong increase in dis solved silicon levels in the sediment porewater. In addition, S. anglica wa s cultured in the laboratory on nutrient solution enriched with dissolved s ilicon. Neither in the field nor in the laboratory experiment did the incre ased silicon levels have effects on shoot growth or led to consistent incre ases in the silicon concentration of plant tissues. Finally, different S. a nglica stands in a number of salt marshes around the Oosterschelde basin we re examined on sediment porewater silicon concentrations and silicon plant tissue concentrations. Sediment porewater silicon levels ranged between 36 and 554 mu M. The average silicon concentration of the shoots from the vari ous populations ranged between 3.52 and 11.73 mg/g DW. Consistent with the results of the field and laboratory experiments, there was no correlation b etween porewater silicon concentrations and average shoot length at the dif ferent sites, nor between porewater silicon concentrations and shoot silico n levels. Apparently, vegetative growth and tissue silicon concentrations o f S. anglica do not respond to concentrations of dissolved Si in the range to which the plants were exposed naturally or experimentally in the field a nd in the laboratory (ca. 15-550 mu M). In the data set pertaining to the d ifferent S. anglica field populations, however, negative correlations were observed between the average number of leaves per shoot at the different lo cations and the total silicon content of the 4th and 2nd leaves and of the entire shoots. The possible mechanisms explaining differences in tissue Si concentrations are discussed.