3D Nanostructures Hit Ryegrass and Soil Microbes Harder Than Flat Sheets

Engineered nanomaterials are quietly spreading through the world’s farmland, and a new 50-day greenhouse experiment suggests that the shape of those tiny particles may matter as much as what they are made of. Researchers at Sun Yat-sen University in Shenzhen grew Italian ryegrass in agricultural yellow soil treated with two forms of nickel-iron layered double hydroxides, or NiFe-based LDHs, a family of metal-based engineered nanomaterials prized for cleaning polluted water and immobilizing soil contaminants. One material was a flat, two-dimensional sheet; the other was a three-dimensional, sulfur-containing flower-like structure assembled from the same chemistry. The difference in architecture produced strikingly different consequences for the plants, the soil chemistry, and the microscopic communities that keep soil alive.

The study, published in Advanced Biotechnology, arrives at a moment of growing anxiety over the ecological footprint of engineered nanomaterials. Layered double hydroxides carry the general formula [M2+1−xM3+x(OH)2]An−x/n·yH2O, and their high surface area, anion exchange capacity, and thermal stability have made them favored adsorbents for heavy metals, dyes, and other pollutants. China’s chemical industry standard HG/T 5549–2019 even recognizes LDHs as an environmentally friendly adsorbent material. But as production volumes climb, so do emissions into the environment, and soil is the compartment where these particles tend to accumulate. Because LDHs can interact directly with cell surfaces, dissolve toxic elements, and generate reactive oxygen species, the team argued that understanding their fate in terrestrial ecosystems is no longer optional.

The researchers synthesized the two-dimensional NiFe-LDHs hydrothermally from ferric chloride and nickel nitrate with urea, and converted part of that product into the three-dimensional NiFeS-LDHs by reacting it with thioacetamide in ethanol. X-ray diffraction and electron microscopy confirmed the structures. Ryegrass, a fast-growing annual grass with high biomass and documented tolerance to heavy metals and nanomaterials, served as the model plant. Pots received 2 kilograms of sieved farmland soil each, amended with either material at concentrations ranging from 200 to 800 milligrams per kilogram, alongside untreated controls, and the plants grew for 50 days before harvest.

The growth results split cleanly along structural lines. Two-dimensional NiFe-LDHs promoted ryegrass growth at specific concentrations: chlorophyll content rose significantly at amendment levels between 200 and 500 milligrams per kilogram compared with untreated soil, and the moderate suppression of fresh weight at 200 milligrams per kilogram gave way to a rebound before declining again at the highest doses. The three-dimensional NiFeS-LDHs told a darker story, significantly reducing fresh weight at every concentration tested and pushing chlorophyll levels below control values at 650 and 800 milligrams per kilogram. Hydrogen peroxide measurements revealed the mechanism at work: both materials triggered oxidative stress, but the 3D particles produced more pronounced accumulation of reactive oxygen species, forcing the plants into a stronger antioxidant response involving catalase, superoxide dismutase, and peroxidase.

Metal uptake analysis helped explain why. Nickel and iron accumulated in ryegrass roots far more than in leaves, and root nickel content was consistently higher in the three-dimensional treatment group than in the two-dimensional group across all concentrations. Nickel is a micronutrient in small doses, supporting urease activity, photosynthesis, and nutrient absorption, but excess nickel disrupts chloroplast function, auxin transport, and iron uptake. At low and moderate concentrations the benefits of trace nickel and iron likely stimulated chlorophyll synthesis, while at high doses metal accumulation overwhelmed those gains and suppressed photosynthesis, a pattern consistent with the hormetic responses seen for other metal-based nanomaterials.

Beneath the surface, the two materials reshaped soil geochemistry in opposite directions. The three-dimensional NiFeS-LDHs significantly lowered soil pH while raising electrical conductivity by as much as 271 percent at 800 milligrams per kilogram. The authors attribute the acidification to sulfide oxidation in the aerated soil, which generates sulfate and hydrogen ions, compounded by hydrolysis of released nickel and iron and by a self-amplifying cycle in which iron-oxidizing microbes regenerate ferric iron that attacks remaining sulfides. The flat sheets behaved more gently, gradually reducing electrical conductivity, likely by adsorbing ions, and stabilizing total carbon and phosphorus. Both materials significantly boosted soil organic carbon, by up to roughly 49 percent for the 2D particles and 56 percent for the 3D particles, while both cut total nitrogen sharply, by 16 to 36 percent depending on dose and material.

Soil enzyme activity, a sensitive barometer of nutrient cycling, diverged along the same structural fault line. The two-dimensional particles suppressed sucrase activity by up to 53 percent at high doses but enhanced urease activity by 25 to 54 percent, leaving catalase and neutral phosphatase largely untouched. The three-dimensional particles did nearly the opposite, significantly inhibiting catalase by 13 to 30 percent and urease by 7 to 29 percent, while boosting neutral phosphatase by roughly 50 to 64 percent at low to moderate doses. These enzymatic fingerprints imply that the two architectures push soil metabolism toward different functional states, with the flat sheets tilting the system toward nitrogen transformation and the structured particles toward phosphorus mobilization at the expense of oxidative and urea-processing capacity.

High-throughput sequencing of 16S rDNA and fungal ITS regions showed that both materials altered the composition of rhizosphere bacterial and fungal communities, but the three-dimensional particles hit harder. At elevated concentrations they significantly depressed fungal diversity indices, a concerning signal because greater fungal diversity has been linked to healthier soils and more sustainable crop production. Moderate concentrations of the 2D particles enriched taxa such as Bryobacter, Flavisolibacter, Rhodoplanes, Cryptococcus, and Fusarium, organisms associated with nitrate reduction, denitrification, plant growth promotion, and stress resistance. Correlation analyses tied these community shifts to soil pH, electrical conductivity, ammonium, and iron levels, and structural equation modeling delivered the study’s headline number: the total negative path coefficient of the 3D material on ryegrass growth through the soil ecosystem, −1.071, was nearly three times that of the 2D material, −0.368, with soil acidification, salt stress, and nickel toxicity acting as the dominant downward forces while the microbial community itself continued to support plant growth.

The findings do not mean that nickel-iron LDHs are unsuitable for environmental work, but they do mean that their ecological risk cannot be assessed by chemistry alone. Two materials with identical elemental composition behaved like entirely different pollutants once their geometry changed, altering enzyme stoichiometry, reshaping microbial assemblages, and shifting the balance of nitrogen and phosphorus cycling. The authors caution that field-scale toxicity will require multi-season trials, ionic and bulk controls, and molecular studies to confirm the causal pathways they observed in pots. Still, as engineered nanomaterials flood into remediation schemes, fertilizers, and wastewater treatment plants, the lesson is blunt and timely: in the soil beneath our feet, nanostructure is destiny, and regulators evaluating the safety of layered double hydroxides would do well to demand the blueprint of every particle before it touches the ground.

Subject of Research: The differential biological effects of 2D and 3D NiFe-based layered double hydroxide nanomaterials on the ryegrass-soil ecosystem.

Article Title: Bio-effects of engineering nanomaterials NiFe-based LDHs on ryegrass-soil system

Article References: Xu, H., Jiang, X., He, C., Peng, Y., Xin, G., & Li, X. (2026). Bio-effects of engineering nanomaterials NiFe-based LDHs on ryegrass-soil system. Advanced Biotechnology, 4(3), Article 24. https://doi.org/10.1007/s44307-026-00114-x

Image Credits: AI Generated

DOI: 10.1007/s44307-026-00114-x

Keywords: engineered nanomaterials, layered double hydroxides, NiFe-LDHs, ryegrass, soil health, soil enzymes, soil microbiome, oxidative stress, soil acidification, fungal diversity, nanotoxicology, soil remediation