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Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soil–plant-microbe cascade
Open accessAbstract
Stabilizing soil lead (Pb) with single amendments often requires a trade-off between immobilization durability and cost-effectiveness, restricting their large-scale use. Here, we demonstrate that co-applying hydroxyapatite (HAP) with either rice straw biochar (RBP) or maize straw biochar (MBP) overcomes these limitations through synergistic soil–plant-microbe interactions. Compared to the un-amended control, the combined treatments reduced CaCl 2 -extractable Pb by 93.2–95.5% and the acid-soluble Pb fraction by 39.4–41.8%. Spectroscopic analyses confirmed the direct binding of Pb to biochar surfaces, while an amendment-induced increase in soil pH further enhanced Pb immobilization. Consequently, this reduced Pb availability in the rhizosphere was associated with diminished iron plaque formation on root surfaces, ultimately decreasing root Pb accumulation. At the subcellular level in leaves, the combined treatments promoted Pb sequestration within vacuoles and reduced the organelle-bound Pb fraction by 16.1–31.9%. This subcellular shift significantly lowered the leaf-to-grain transfer factor by 49.4–54.3%. Furthermore, the combined treatments (RBP) enhanced soil bacterial alpha diversity and shifted community composition; notably, the enrichment of Bacteroidota and suppression of Desulfobacterota suggest their potential contribution to further Pb stabilization. Through these integrated mechanisms, Pb concentrations in brown rice were reduced below Chinese national food safety limits. These findings highlight that the co-application of biochar and HAP provides a cost-effective, multi-barrier strategy to mitigate soil-to-grain Pb transfer, enabling the sustainable utilization of Pb-contaminated paddy soils.
Overview
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TL;DR
Co-applying hydroxyapatite with rice or maize straw biochar suppressed Pb availability and rice grain accumulation through soil immobilization, reduced root iron plaque, leaf vacuolar sequestration, and shifts in rhizosphere bacteria. In pot trials, combined treatments reduced CaCl2-extractable Pb by 93.2–95.5% and grain Pb to 0.077–0.091 mg/kg, below the 0.2 mg/kg limit.
Key findings
- Combined RBP and MBP treatments reduced CaCl2-extractable Pb by 93.2–95.5% and the acid-soluble Pb fraction by 39.4–41.8% versus the un-amended control; XANES indicated 32.9% of soil Pb in the biochar-amended treatment was associated with the biochar matrix.
- Iron plaque DCB-Pb was reduced by the combined treatments; the Results report decreases of 53.46% (RBP) and 61.39% (MBP), while the Discussion reports 61.4% (RBP) and 46.3% (MBP). Root Pb at maturity decreased by 52.6% and 38.4% under RBP and MBP, respectively.
- Leaf organelle-bound Pb decreased by 16.1–31.9%, and the leaf-to-grain transfer factor decreased by 49.4–54.3%. Brown rice Pb was 0.077 mg/kg (RBP) and 0.091 mg/kg (MBP) versus 0.22 mg/kg in the control; grain yield increased by 62.0–72.6% under combined treatments.
- RBP increased OTUs by 42.38%, ACE by 46.09%, Chao1 by 43.19%, and Shannon by 6.80%; Bacteroidota increased from 0.12% to 4.97%, while Desulfobacterota decreased from 1.67% to 0.54%.
Methods
- Pot experiment with six treatments in triplicate: un-amended control (CK), 2.5% rice straw biochar (RB), 2.5% maize straw biochar (MB), 0.6% hydroxyapatite (P), RBP, and MBP. Soil was from a mining-area farmland in Youxi County, Fujian, China, with initial Pb approximately 1699.2 mg/kg; rice cultivar Donglian 5 was sampled at tillering (60 days) and maturity (132 days).
- Analyses included soil pH, EC, Eh, SOM, N, C/N, CaCl2- and DTPA-extractable Pb, BCR sequential extraction, Pb L3-edge XANES, DCB-extractable Fe/Mn/Pb in iron plaque, tissue Pb by ICP-MS, leaf subcellular Pb fractions, and full-length 16S rRNA PacBio sequencing for CK, RB, P, and RBP at 45 days after flooding. Statistics used one-way ANOVA, Mantel tests, RDA, and Chao1/Shannon/ACE diversity indices.
Limitations
- Paper-stated: only one rice cultivar was tested; the initial soil Pb concentration (about 1699.2 mg/kg) is representative of severely contaminated mining-area paddy fields but higher than most agricultural soils, limiting direct generalizability. Future work is needed across Pb gradients, multiple cultivars, long-term field conditions, co-contaminants, and fluctuating redox conditions.
- Paper-stated: microbial sequencing covered only CK, RB, P, and RBP, not MBP; Bacteroidota EPS production, Pb-binding capacity, in situ Pb speciation, sulfur speciation, and sulfide production were not directly measured, so those microbial mechanisms remain correlative or hypothetical.
- Evident from the text: DCB-Pb reduction magnitudes are inconsistent between the Results and Discussion; the study is a pot experiment with one soil and short-term sampling, which limits field extrapolation.
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0 Valid · 1 Not valid · 19 Not checked · 75 Own results and interpretations
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In the paper
“The application of biochar, either alone or combined with HAP, significantly reduced Fe and Mn concentrations in the iron plaque compared to the control (Fig. 3a, b)”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > A R T I C L E I N P R E S S
plainstates a cause- Asserted: passes — The authors put it forward as true.
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In the paper
“the relative abundance of Hungateiclostridiaceae was higher in the RB, P, and RBP treatments than in the CK group.”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > 3.6 Effects on soil bacterial community diversity
plainstates an association- Asserted: passes — The authors put it forward as true.
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In the paper
“DCB-Pb was negatively correlated with the abundances of Chloroflexi, Myxococcota, and Bacteroidota.”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > 3.7 Impact of environmental factors on microbial communities
plainstates an association- Asserted: passes — The authors put it forward as true.
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In the paper
“Spectroscopic analyses confirmed the direct binding of Pb to biochar surfaces”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > Abstract
plainstates a cause- Asserted: passes — The authors put it forward as true.
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In the paper
“the RBP and MBP treatments elevated the C/N ratio by approximately 55.1% and 53.3%, respectively”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > A R T I C L E I N P R E S S
plainstates a cause- Asserted: passes — The authors put it forward as true.
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- Load-bearing: unclear — It is unclear whether the paper’s conclusions depend on it.
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In the paper
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > 3.3. Pb concentration in iron plaque
“Compared to the control, the combined biochar and HAP treatments achieved the greatest reductions in DCB-Pb, with decreases of 53.46% and 61.39% observed in the RBP and MBP treatments, respectively.”
§ Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soilplant-microbe cascade > 4.2. Mitigation of Pb uptake by suppressing root iron plaque formation
“This decline was closely linked to reduced Pb sequestration within the root iron plaque, evidenced by decreases in DCB-Pb of 61.4% (RBP) and 46.3% (MBP) (Fig. 3c).”
Cited works that were retracted
Works this paper cites that were later retracted, from the retraction notices publishers deposit. Major when the notice came out before this paper was published.
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In the paper
“Bolan, S. et al. Biochar modulating soil biological health: A review. Sci. Total Environ. 914, 169585. https://doi.org/10.1016/j.scitotenv.2023.169585 (2024).”
Cited work 10.1016/j.scitotenv.2023.169585 · retracted 2026-06-30 · notice 10.1016/j.scitotenv.2026.182002 · this paper published 2026-07-14
Citations
Cites
1 retracted
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Research works printed but not linked: 1
- Li, H. . et al. Antagonistic effects of exogenous zinc on uptake and accumulation of cadmium in various rice organs. Acta Sci. Circumst. 38, 4854–4863. https://doi.org/10.13671/j.hjkxxb.2018.0356 (2018). · doi:10.13671/j.hjkxxb.2018.0356
Cited by
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Metadata
- Authors
- Li, H., Khaliq, M. A., Long, J., Wang, G., & Li, Z.
- Affiliations
- Fujian Agriculture and Forestry University (CN)
- Minnan Normal University (CN)
- Fujian Academy of Agricultural Sciences (CN)
- Corresponding author
- Wang, Guo
- Li, Zhou
- ORCID
- Wang, Guo
- Venue
- Scientific Reports
- Published
- 2026-07-14
- Volume
- 16
- Issue
- 1
- ISSN
- 2045-2322 (ISSN-L)
- OpenAlex
- W7168253562
- Semantic Scholar
- c0f3d775a76d9ae1353e0480550a0120c7e52a55
- Cited by
- 0
- References
- 67
- FWCI
- 0.00
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by-nc-nd
- creativecommons.org/licenses/by-nc-nd/4.0 (tdm)
- creativecommons.org/licenses/by-nc-nd/4.0 (vor, 92 d)
- Locations
- Scientific Reports (publishedVersion, cc-by-nc-nd)
- PubMed (publishedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
- Funders
- Natural Science Foundation of Fujian Province (2025J01984, 2023J01373)
- Natural Science Foundation of Zhangzhou City (ZZ2023J12)
- Topics
- Physical Sciences › Environmental Science › Pollution › Heavy metals in environment
- Physical Sciences › Environmental Science › Water Science and Technology › Adsorption and biosorption for pollutant removal
- Physical Sciences › Environmental Science › Health, Toxicology and Mutagenesis › Chromium effects and bioremediation
- Keywords
- lead immobilization, biochar, hydroxyapatite, rice, plant-soil-microbe interactions, iron plaque, soil bacterial communities, paddy soil remediation, lead-contaminated soil, straw biochar, transfer factor, food safety
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- CoChat. (2026). Citation check: Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soil–plant-microbe cascade. https://app.cochat.ai/papers/10.1038/s41598-026-62191-1
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- Li, H., Khaliq, M. A., Long, J., Wang, G., & Li, Z. (2026). Co-application of biochar and hydroxyapatite suppresses lead accumulation in rice via a soil–plant-microbe cascade. Scientific Reports. https://doi.org/10.1038/s41598-026-62191-1
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