No abstract

Silicon (Si) is not classified as an essential element for plants, but numerous studies have demonstrated its beneficial effects in a variety of species and environmental conditions, including low nutrient availability. Application of Si shows the potential to increase nutrient availability in the rhizosphere and root uptake through complex mechanisms, which still remain unclear. Silicon-mediated transcriptional regulation of element transporters for both root acquisition and tissue homeostasis has recently been suggested as an important strategy, varying in detail depending on plant species and nutritional status. Here, we summarize evidence of Si-mediated acquisition, uptake and translocation of nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chlorine (Cl), and nickel (Ni) under both deficiency and excess conditions. In addition, we discuss interactions of Si-with beneficial elements: aluminum (Al), sodium (Na), and selenium (Se). This review also highlights further research needed to improve understanding of Si-mediated acquisition and utilization of nutrients and vice versa nutrient status-mediated Si acquisition and transport, both processes which are of high importance for agronomic practice (e.g., reduced use of fertilizers and pesticides).

The beneficial effects of silicon (Si) have been shown on plants using reduction-based strategy for iron (Fe) acquisition. Here we investigated the influence of Si on Fe deficiency stress alleviation in barley ( Hordeum vulgare ), a crop plant which uses the chelation-based strategy for Fe acquisition. Analyses of chlorophyll content, ROS accumulation, antioxidative status, concentrations of Fe and other micronutrients, along with the expression of Strategy II genes were studied in response to Si supply. Si successfully ameliorated Fe deficiency in barley, diminishing chlorophyll and biomass loss, and improving the activity of antioxidative enzymes, resulting in lowered reactive oxidative species accumulation in the youngest leaves. Alleviation of Fe deficiency stress correlated well with the Si-induced increase of Fe content in the youngest leaves, while it was decreased in root. Moreover, Si nutrition lowered accumulation of other micronutrients in the youngest leaves of Fe deprived plants, by retaining them in the root. On the transcriptional level, Si led to an expedient increase in the expression of genes involved in Strategy II Fe acquisition in roots at the early stage of Fe deficiency stress, while decreasing their expression in a prolonged stress response. Expression of Strategy II genes was remarkably upregulated in the leaves of Si supplied plants. This study broadens the perspective of mechanisms of Si action, providing evidence for ameliorative effects of Si on Strategy II plants, including its influence on accumulation and distribution of microelements, as well as on the expression of the Strategy II genes.

The results suggest that Si enhances remobilization of Fe from older to younger leaves by a more efficient NA-mediated Fe transport via the phloem. In addition, from this and previous work, a model is proposed of how Si acts to improve Fe homeostasis under Fe deficiency in cucumber.

Failures of tailings dams have degraded large areas of agricultural alluvial soils worldwide, and concomitant soil pollution studies are abundant. Yet, the data on the actual effects of thereby imposed stresses on major crops are scarce. This work analyses the effect of pyrite tailings from a copper mine, deposited over crop fields by long-term flooding, on wheat (Triticum aestivum L.) under field conditions. The major previously reported polluting agents were Cu, As, Zn, Pb and acidity generated by sulphide oxidation. Flexible systematic sampling, based on visual symptoms in wheat, included transects through partially damaged fields (from calcareous to acid soils). Multivariate analysis of soil properties, leaf mineral composition and growth parameters revealed a consistent underlying soil gradient of decreasing available P and increasing S tot . Phosphorus was shown to have the highest unique contribution to predicting wheat yield, consistent correlation with growth and visual symptoms, and concentrations in the range of severe deficiency. In P deficient plants N deficiency, decrease of available micronutrients and increase of As occur irrespectively of their soil concentrations, and the competition with superior "pyrite" weeds increases. Different sorption of P and possible rhizotoxic effects of other pollutants imply that fertilization can hardly be a solution.