Abstract
Plants can take up significant amounts of silicon (Si), which is deposited in the apoplast as silica (SiO2). Changes in biomass and element concentrations after Si application often have been attributed to direct effects of Si on photosynthesis and nutrient uptake, not accounting for the significant biomass effect of SiO2 which dilutes biomass and element concentrations. Here, we quantified this biomass dilution by SiO2 and its effect on the interpretation of element concentrations. Five independent hydroponic experiments with rice, wheat, and rapeseed were conducted at different Si supply levels (0-2000 & micro;mol L-1). Biomass and element concentrations were determined (measured data) and mathematically corrected for the SiO2 content of the biomass (SiO2-free estimate data). With increasing Si supply, measured carbon concentrations were significantly reduced by up to 6%. This effect disappeared after mathematical correction of the SiO2 dilution. Similar results were found for elements with predominantly transporter-mediated uptake. For sodium, an element taken up via bypass flow, relative concentration changes attributable to mere biomass dilution were strongly outweighed by other effects. This shows that SiO2 deposition mechanistically alters the uptake processes of this element. These results illustrate that meaningful analysis of changes in nutrient uptake patterns due to Si can only be done after accounting for SiO2 dilution. Not correcting the concentrations of elements by SiO2 dilution can lead to a misinterpretation of the nutritional status of plants.