Precipitation versus dissolution at the phosphorus and Solanum nigrum L. root exudate interface: Implications for lead rebound in rhizosphere soils

• Published in: The Science of the total environment 2024-12, Vol.957, p.177453, Article 177453
• Main Authors: Zhang, Jingwei, Shi, Hao, Xing, Yiquan, Chen, Yixin, Li, Jiacheng, Fu, Haojie, Dai, Guoqing, Cui, Zhaojie, Wang, Lei, Li, Xinxin
• Format: Article
• Language: English
• Subjects: Dissolution; Lead - metabolism; Lead rebound; Phosphorus; Plant Exudates - chemistry; Plant Roots; Precipitation; Rhizosphere; Root exudates; Soil - chemistry; Soil microbial function; Soil Microbiology; Soil Pollutants - metabolism; Solanum nigrum
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.177453

Lead (Pb) rebound in the root-zone of plants is a primary risk associated with rhizosphere effect in phosphorus (P)-amended vegetated soils. Herein, we investigated the differential effects of root exudates (RE) from Solanum nigrum L. on Pb availability under conditions with variable P mineral forms. Batch precipitation-dissolution tests verified the addition of RE to the soils boosted Pb release and lowered the utilization efficiency of P as a result of favoring Pb retention in soil solid phases. Typically, oxalate, selected as a representative RE composition, significantly enhanced Pb release after being immobilized with highly soluble phosphate (NaH2PO4), but no detectable Pb for the treatments with low P-solubility hydroxypyromorphite (Pb5(PO4)3OH). Sequential extraction results revealed that a portion of released Pb was re-adsorbed onto the soil surfaces after adding P, while the presence of oxalate increased the dissolution risk associated with residual Pb and organic P due to the soil pH-induced effects. Further morphological analyses revealed that the solid-to-liquid partitioning of Pb was largely dependent upon the P-induced precipitation and RE-induced dissolution reactions. Both P and RE reduced the negative effect of Pb on soil microbial activity by recruiting more plant-growth-promoting and reactive oxygen species-generating genera, e.g., Firmicutes and Actinobacteria, thus facilitated microbial resistance to Pb in near-rhizosphere soil. These findings highlight the role of P-based treatments in altering the rhizosphere-mediated Pb rebound with biotic and abiotic interaction for remediation of Pb-contaminated soils. [Display omitted] •Interaction between P-bearing minerals and root exudates resulted in Pb rebound.•P addition to soil favored Pb precipitation as PbP minerals, for example, HPM.•Root exudates favored PbP mineral dissolution and Pb release into soil solution.•Labile Pb transformation is largely attributed to soil pH-induced effect.•The role of microbial communities in regulating Pb availability is reconfirmed.