Zinc and Silicon Nano-Fertilizers Influence Ionomic and Metabolite Profiles in Maize to Overcome Salt Stress

Abstract

Salinity stress is a major factor affecting the nutritional and metabolic profiles of crops, thus hindering optimal yield and productivity. Recent advances in nanotechnology propose an avenue for the use of nano-fertilizers as a potential solution for better nutrient management and stress mitigation. This study aimed to evaluate the benefits of conventional and nano-fertilizers (nano-Zn/nano-Si) on maize and subcellular level changes in its ionomic and metabolic profiles under salt stress conditions. Zinc and silicon were applied both in conventional and nano-fertilizer-using farms under stress (100 mM NaCl) and normal conditions. Different ions, sugars, and organic acids (OAs) were determined using ion chromatography and inductively coupled plasma mass spectroscopy (ICP-MS). The results revealed significant improvements in different ions, sugars, OAs, and other metabolic profiles of maize. Nanoparticles boosted sugar metabolism, as evidenced by increased glucose, fructose, and sucrose concentrations, and improved nutrient uptake, indicated by higher nitrate, sulfate, and phosphate levels. Particularly, nano-fertilizers effectively limited Na accumulation under saline conditions and enhanced maize's salt stress tolerance. Furthermore, nano-treatments optimized the potassium-to-sodium ratio, a critical factor in maintaining ionic homeostasis under stress conditions. With the growing threat of salinity stress on global food security, these findings highlight the urgent need for further development and implementation of effective solutions like the application of nano-fertilizers in mitigating the negative impact of salinity on plant growth and productivity. However, this controlled environment limits the direct applicability to field conditions and needs future research, particularly long-term field trials, to confirm such results of nano-fertilizers against salinity stress and their economic viability towards sustainable agriculture.

Keywords: apoplast; ionomic; metabolites; molecular; nano; physiology; salinity; subcellular level; symplast.

Figure 1

Sodium in shoot and root (a,b), potassium in soot and root (c,d), K/Na ration in shoot and root (e,f) and zinc in shoot and root (g,h) of maize plant under saline and non-saline soil (100 mM NaCl) along with exogenous application of Zn@100 ppm and Si@90 ppm both as conventional fertilizers (ZnSO₄ and K₂SiO₃) and nanofertilizers (ZnO and SiO₂). Means with distinct letters differ significantly (LSD test; p < 0.05).

Figure 2

Nitrate, sulphate, phosphate, and chloride in apoplast (a,c,e,g) and symplast (b,d,f,h) of maize plant under salt (100 mM NaCl) stress with the application of Zn@100 ppm and Si@90 ppm both as conventional fertilizers (ZnSO₄ and K₂SiO₃) and nano-fertilizers (ZnO, SiO₂). Means with distinct letters differ significantly (LSD test, p < 0.05).

Figure 2

Nitrate, sulphate, phosphate, and chloride in apoplast (a,c,e,g) and symplast (b,d,f,h) of maize plant under salt (100 mM NaCl) stress with the application of Zn@100 ppm and Si@90 ppm both as conventional fertilizers (ZnSO₄ and K₂SiO₃) and nano-fertilizers (ZnO, SiO₂). Means with distinct letters differ significantly (LSD test, p < 0.05).

Figure 3

Sodium, potassium, zinc, and silicon concentrations in apoplast (a,c,e,g) and symplast (b,d,f,h) of maize plant under salt stress (100 mM NaCl) with the application of Zn@100 ppm and Si@90 ppm both as conventional fertlizers (ZnSO₄ and K₂SiO₃) and nanofertlizers (ZnO, SiO₂). Means with distinct letters differ significantly (LSD test, p < 0.05).

Figure 4

Glucose, fructose, and sucrose concentrations in apoplast (a,c,e) and symplast (b,d,f) of maize plant under saline and non-saline soil (100 mM NaCl) along with exogenous application of Zn@100 ppm and Si@90 ppm both as conventional fertilizers (ZnSO₄ and K₂SiO₃) and nanofertlizes (ZnO and SiO₂). Means with distinct letters differ significantly (ANOVA, LSD, p < 0.05; SE bars, n = 3).

Figure 5

Malic acid, citric acid, and oxalates in apoplastic (a,c,e) and symplastic (b,d,f) of maize leaf fractions under normal and saline (100 mM NaCl) conditions along with the exogenous application of Zn@100 ppm and Si@90 ppm both as conventional fertlizers (ZnSO₄ and K₂SiO₃) and nanofertilizers (ZnO and SiO₂). Means with distinct letters differ significantly (ANOVA, LSD, p < 0.05; n = 3).

Figure 6

Relationship heatmap of ions in leaves. The figure includes potassium in roots (K.R.), potassium in shoots (K.S.), the potassium–sodium ratio in shoots (K.Na.S), the potassium–sodium ratio in roots (K.Na.R), silicon in shoots (Si.S), zinc in shoots (Zn.S), sodium in roots (Na.R), sodium in shoots (Na.S), sulfate in shoot (SO₄.S), nitrate in shoot (NO₃.S), phosphate in shoot (PO₄.S), and chloride in shoot (Cl.S.).

Figure 7

Comparative heatmaps of citric acid (C.A), malic acid (M.A), oxalic acid (O.A), glucose (Gluc), fructose (Fruc), and sucrose (Sucr) in the apoplast (A) and symplast (B) of plants treated with conventional and nanofertilizers of Zinc and Silicon.

Figure 8

Correlation matrix of ions in plant tissues under saline and non-saline conditions. This figure includes potassium in roots (K.R.), potassium in shoots (K.S.), potassium–sodium ratio in shoots (K.Na.S), potassium–sodium ratio in roots (K.Na.R), silicon in shoots (Si.S), zinc in shoots (Zn.S), sodium in roots (Na.R), and sodium in shoots (Na.S). The annotations of *, **, *** on Correlation values represents significance at probability level of 0.1, 0.05 and 0.01 respectively.