Iron-modified biochar modulates root metabolism, mitigates antimony accumulation and enhances growth in rice (Oryza sativa)

Abstract

Background: Antimony (Sb), with low biodegradability and high bioavailability in plants, poses significant health risks via the food chain due to its chronic toxicity and carcinogenicity. Modified biochar represents a promising amendment for ecological remediation of metal-contaminated croplands, yet the efficacy and mechanisms of its application in mitigating Sb accumulation and improving plant growth in Sb-polluted agricultural systems remain inadequately elucidated and require systematic investigation.

Results: In this study, pristine biochar (BC) and iron-modified biochar (FeBC) were prepared from pomelo peel flesh (PPF; Citrus maxima), and their effects on rice root growth, Sb content, and metabolism under 30 mg/L Sb stress were evaluated. Treatment with 5 g/L BC and 5 g/L FeBC increased root length by 35.04% and 84.60%, respectively, while reducing Sb accumulation in roots by 25.79% and 28.03%, respectively. Root metabolite analysis showed that, compared to BC, FeBC significantly decreased levels of p-coumaroylagmatine, silibinin, and osmanthuside A by 75%, 37%, and 37%, respectively. Conversely, FeBC elevated levels of (S)-actinidine, phaeophorbide A, and 2-keto-6-acetamidocaproate by 187%, 156%, and 122%, respectively. These altered metabolites were enriched in five key metabolic pathways: phenylalanine, tyrosine, and tryptophan biosynthesis; phenylalanine biosynthesis; lysine degradation; tryptophan metabolism; and pantothenate and CoA biosynthesis. Correlation analysis demonstrated significant interrelationships among biochar-induced metabolites, root growth, and Sb accumulation dynamics under Sb stress.

Conclusions: The findings provided the insights that FeBC enhanced rice root metabolism and growth while reducing root Sb accumulation. This study provided a methodological foundation for developing eco-friendly remediation technologies in Sb-contaminated soils to enable safer and more sustainable rice production.

Keywords: Antimony; Iron-modified biochar; Pristine biochar; Root growth; Root metabolism.

Fig. 1

Scanning electron microscopy images showing morphological differences between BC (a, c, e) and FeBC (b, d, f). Scale bars were 20 μm (a, b), 5 μm (c, d), and 500 nm (e, f), respectively

Fig. 2

Elemental composition analysis of FeBC by EDS. A EDS image of FeBC; B an electron microscope image of FeBC; C the elemental distribution of magnetic biochar. Scale bars in B and C were both 5 µm

Fig. 3

Spectroscopic analysis showing A BC and B FeBC by FTIR, with C crystalline structure of FeBC by XRD

Fig. 4

Impact of biochar and iron-modified biochar on rice root growth and antimony accumulation. The length of rice in 0 mg/L (A) and 30 mg/LSb exposure (B). Sb contents of the rice root in 30 mg/L Sb exposure (C)

Fig. 5

Partial least squares discriminant analysis (PLS-DA) score plots (A and B) and corresponding validation plots for BC and FeBC in both positive (NT-pos) (C) and negative (NT-neg) (D) ionization modes

Fig. 6

Comparative metabolomics using volcano plots demonstrating differential root metabolites between (A) CK and BC, (B) CK and FeBC, and (C) BC and FeBC treatment groups

Fig. 7

KEGG pathway analysis of root metabolites showing differential regulation between A CK and BC, B CK and FeBC, and C BC and FeBC treatment groups. (1) betalain biosynthesis, (2) starch and sucrose metabolism, (3) pantothenate and CoA biosynthesis, (4) biotin metabolism, (5) lysine degradation, (6) phenylalanine, tyrosine and tryptophan biosynthesis, (7) tropane, piperidine and pyridine metabolism, (8) phenylpropanoid biosynthesis, (9) galactose metabolism, (10) valine, leucine and isoleucine biosynthesis, (11) arginine biosynthesis, (12) arginine and proline metabolism, (13) lysine biosynthesis, (14) arachidonic acid metabolism, (15) tryptophan metabolism

Fig. 8

A comprehensive overview of treatment-induced alterations in root metabolome