Stimulation of peanut seedling development and growth by zero-valent iron nanoparticles at low concentrations

Abstract

Because of its strong pollutant degradation ability, nanoscale zerovalent iron (NZVI) has been introduced to soils and groundwater for remediation purposes, but its impacts on plants are still not very clear. In this work, the effects of low concentration (10-320 μmol/L) NZVI particles on seed germination and growth of peanut plants were evaluated. The exposure of peanut seeds to NZVI at all the tested concentrations altered the seed germination activity, especially the development of seedlings. In comparison with the deionized water treated controls (CK), all of the NZVI treatments had significantly larger average lengths. Further investigations with transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) suggested that NZVI particles may penetrate the peanut seed coats to increase the water uptake to stimulate seed germination. The growth experiments showed that although NZVI at a relatively high concentration (320 μmol/L) showed phytotoxicity to the peanut plants, the lower concentrations of NZVI particles stimulated the growth and root development of the plants. At certain concentrations (e.g., 40 and 80 μmol/L), the NZVI treated samples were even better than the ethylenediaminetetraacetate-iron (EDTA-Fe) solution, a commonly used iron nutrient solution, in stimulating the plant growth. This positive effect was probably due to the uptake of NZVI by the plants, as indicated in the TEM analyses. Because low concentrations of NZVI particles stimulated both the seedling development and growth of peanut, they might be used to benefit the growth of peanuts in large-scale agricultural settings.

Fig 1. TEM (a) and XRD (b) analyses of NZVI.

Fig 2. Effects of NZVI treatments on peanut seed germination.

a) reprehensive photograph of seeds after 2 days, b) reprehensive photograph of seedlings after 4 days, c) length of the seedlings after 4 days, and d) TGA analyses of selected seeds after 2 days. Different letters show significant differences (p⩽0.05) and bars represent the standard error of treatments (n = 4). NZVI was indicated by dark arrow.

Fig 3. TEM analyses of peanut seeds after 4 days.

a) seed coat of NZVI-40, b) seed coat of CK, c) peanut of NZVI-40, and d) peanut of CK. The dark arrows show small clusters of NZVI particles. NZVI was indicated by dark arrow.

Fig 4. Effects of NZVI treatments on peanut plant growth.

a) photograph of peanut plants in containers after 13 days, b) photograph of peanut plants after 18 days, c) length of the stems of the peanut plants, d) weight of the peanut plants, e) TEM image of root tissue of NZVI-40, and f) TEM image of root tissue of CK. Different letters show significant differences (p⩽0.05) and bars represent the standard error of treatments (n = 4). NZVI was indicated by dark arrow.

Fig 5. Images of roots of peanuts with different NZVI treatments.