Effects of SiO2 nanoparticles on root structures, gas exchange, and antioxidant activities of Cunninghamia lanceolata seedlings under drought stress

Increasing evidence shows that silicon possesses important physiological functions in plants, thus, silicon fertilizers are used widely in agriculture. However, few attentions were paid on the effects of silicon dioxide nanoparticles (SiO2NPs) on plant growth and resistance to abiotic stresses. In this present study, different amount of SiO2NPs were applied in pots with Cunninghamia lanceolata seedlings, and their root development, gas exchange, and drought resistance were investigated. These results showed that SiO2NPs treatment increased total root length, root volume, and the numbers of root tips of these seedlings under drought stress. Specific root area (SRA) and specific root length (SRL) also increased. SiO2NPs treatment altered anatomical structures of the first-order lateral roots of C. lanceolata seedlings under drought stress (i.e., increase in cortex thickness and the number of cortex layers). Under drought stress, SiO2NPs treatment increased net photosynthetic rates, stomatal conductance, intercellular CO2 concentration, and transpiration. SiO2NPs treatment also led to increase in light use efficiency and instantaneous Rubisco carboxylation rate and decrease in water use efficiency under drought stress. Under drought stress, SiO2NPs treatment resulted in increased activities of antioxidant enzymes (superoxide dismutase, catase, and peroxidase) and concentrations of antioxidants (ascorbate and glutathione), decreasing oxidative damage caused by drought stress. All together, these results suggested that SiO2NPs could be used for seedling culture of forest trees.