Effects of silicon application on <i>Betula pendula</i> seedlings

Silicon (Si) is a beneficial element for many plant species, conferring resistance to drought and herbivory, but its effects on trees are less known. We studied responses of silver birch ( Betula pendula), grown in peat, to liquid Si supplementation (Si concentration 0.65 mmol/L) on (1) growth, (2) water economy, and (3) element accumulation plus (4) feeding preference of an insect, Epirrita autumnata, and a mammalian herbivore, Microtus agrestis. Plant growth was not affected but control (Si–) plants shed their old leaves earlier. Detached Si+ leaves lost water 11% units less than Si–, and the integrated water-use efficiency based on 13 C analysis was higher in Si+. Foliar Se was higher and Mn and S lower in Si+. Root Mg concentrations were higher and Pb lower in Si+. Epirrita autumnata did not prefer either treatment, but M. agrestis preferred Si– stems. Silicon improved birch water relations as indicated by the leaf drying resistance and increased water-use efficiency. The changes in metal accumulation were probably beneficial, but the lower S/Se ratio requires attention. Furthermore, Si decreased palatability to a mammalian herbivore. Using Si as fertilizer in nurseries could be possible to increase birch tolerance to water stress and herbivory.