Effects of silicon nanoparticles on growth and physiology of wheat in cadmium contaminated soil under different soil moisture levels.

Soil degradation with different stress conditions like accumulation of cadmium (Cd) contents in soil and drought stress has become one of the most dangerous issues that obstruct the sustainable agriculture production. Silicon nanoparticles (Si NPs) play beneficial roles in combating various biotic and abiotic stresses but their role under combined metal and drought stress is not studied. A pot study was designed to determine the effect of Si NPs on wheat (Triticum aestivum L.) growth and uptake of Cd grown in Cd contaminated soil with different water levels under ambient conditions. Four different levels of Si NPs (0, 25, 50, and 100 mg/kg) were applied in the soil before 1 week of wheat sowing and two water levels (70% and 35% soil water-holding capacity) were introduced after 50 days of seed sowing for the remaining growth period. The lowest biomass, yield, and photosynthesis were observed in the control plants while oxidative stress and the highest Cd concentrations in shoots, roots, and grains were observed in the control plants, and the drought stress further enhanced this effect on the plants. The Si NPs treatments improved the plant growth indicators and photosynthesis, and reduced the Cd concentrations in wheat tissues, especially in grains either without or with drought stress. The Si NPs reduced the oxidative stress in leaves as was indicated by the reduced production of hydrogen peroxide, electrolyte leakage, and malondialdehyde contents, and increase in superoxide dismutase and peroxidase activities. The improvement in wheat growth and a reduction in oxidative stress and Cd concentration in tissues were dependent on the levels of Si NPs and the effect was the highest with the highest level of NPs used.