Nanosilicon Particle Effects on Physiology and Growth of Woody Plants

Abstract

Nanoparticles can influence key physiological processes including seed germination, photosynthesis, and thereby plant growth and yield. Despite several studies have addressed the effects of nanoparticles on crops, data for woody plant species is still scarce. In this report, the effects of silicon dioxide nanoparticles (SiO2 NPs) application, as potentially toxic elements, on physiological performance of 1-year-old woody plants, namely, hawthorn (Crataegus aronia L.) and mahaleb (Prunus mahaleb L.), were evaluated. Plants were irrigated with different concentrations of SiO2 NPs (0, 10, 50, and 100 mg L−1) for 45 days, and gas exchange parameters, relative water content (RWC), xylem water potential, growth, biomass allocation, and nutrient balance were recorded. Si concentration in leaves and its presence over the root surface were analyzed by XRF and SEM, respectively. Results showed diminishing RWC and xylem water potential with the increasing concentrations of SiO2 NPs, thereby confirming detrimental effects of SiO2 NPs irrigation on water status of the plants. Despite the poorer water status, photosynthesis rate (A), stomatal conductance (g s), and transpiration rate (E) were not affected by SiO2 NPs treatments but improved marginally in both species. Overall, the application of SiO2 NPs slightly enhanced plant growth in both species, more evidently in hawthorn, particularly because roots were benefited in growth and length. The presence of SiO2 NPs on the root surfaces was pragmatic in both the species using SEM. XRF analysis of the leaf tissue confirmed that Si concentration in leaf tissues increased at increasing levels of SiO2 NPs, whereas concentrations of examined macronutrients, i.e., nitrogen, phosphorus, and potassium, remain unaffected at increasing levels of SiO2 NPs application. In conclusion, although water status of the woody plants was slightly disrupted by SiO2 NPs, such negative effects were not reflected on plant physiological performance. Therefore, the results should be carefully interpreted as current research reveals that SiO2 NPs application to a certain extent can (contrary to expected) aid slight improvement in leaf physiological performance as well as in root elongation, finally contributing to enhanced plant growth. However, toxic effects, as exhibited by exposure of longer duration and/or higher concentrations of SiO2 NPs, cannot be ruled out in plants, a topic that unavoidably merits further experimental investigation in woody species.