article · Ecotoxicology and Environmental Safety
This study examined how the plant Phytolacca icosandra and its root-associated microbes respond to soil manganese contamination. Seedlings grown for three months under varying manganese concentrations revealed that very high exposure, specifically at 2500 and 5000 micrograms per gram, significantly reduced root and shoot biomass. Despite this growth reduction, the plant continued to absorb excess manganese across its tissues. At the highest manganese levels, chlorophyll a and malondialdehyde concentrations decreased, preventing leaf cell membrane degradation. High manganese exposure also led to increased rhizosphere acidification and decreased soil nitrogen bioavailability. Furthermore, metagenomic analysis revealed distinct shifts in root-associated bacterial communities, with certain species declining while others, such as Tumebacillus avium and Devosia riboflavina, increased in abundance. These combined plant and microbial responses offer biological insights into the remediation of manganese-contaminated agricultural soils.
Manganese pollution can degrade agricultural lands and disrupt soil ecosystems. By identifying how specific plants tolerate high metal levels and how rhizosphere bacteria adapt to extreme contamination, this research highlights natural biological processes that can inform soil recovery strategies and identify useful microbial indicators for monitoring contaminated farmlands.
The findings could inform environmental remediation programmes and agricultural soil management initiatives seeking plant and microbial solutions for heavy metal contamination. Potential end users include environmental remediation specialists and agricultural land managers. This work represents early-stage experimental research, as it demonstrates biological decontamination mechanisms and candidate microbial biomarkers under controlled testing rather than providing a tested field-ready product or service.
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The role of microbial metagenomics in understanding ecological changes associated with rhizosphere heavy metal decontamination by plants has often been overlooked. The aim of this study was to scrutinize the structural, enzymological and metagenomic mechanisms leading to manganese (Mn) decontamination in the rhizosphere by Phytolacca icosandra. Seedlings of P. icosandra were planted for three months under six sets of Mn treatment (addition of 0, 250, 500, 100, 2500, and 5000 µg/g Mn in original soils) using a complete randomized block design. When Mn addition increased to 2500 and 5000 µg/g, the shoot biomass of P. icosandra was reduced by 3.14% and 51.85% respectively, while root biomass was reduced by 5.91% and 47.29% respectively. When Mn uptake increased in the roots/shoots and leaves after the addition of 5000 µg/g Mn, plant chlorophyll a, and malondialdehyde (MDA) concentrations decreased by 4% and 17% respectively. As a result, lipids in the cell membranes of the leaves were no longer destroyed and cell membrane degradation was inhibited by Mn gradients. With addition of 2500-5000 µg/g Mn, the overall weight and height biomasses of P. icosandra was reduced in size to absorb excess Mn. Soil N bioavailability decreased the most at the highest Mn concentration. Above 2500 µg/g Mn, rhizosphere acidification increased (pH < 7). The abundances of rhizosphere bacteria Ramlibacter sp. and Planctomycetaceae bacterium LX124 decreased when soil Mn concentration increased, while those of Tumebacillus avium, Devosia riboflavina, and Flavobacterium fevense increased, paving the way towards microbial biomarkers of soil Mn decontamination. These findings provide valuable knowledge on remediating heavy metal-contaminated agricultural soils.
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DOI: 10.1016/j.ecoenv.2025.118970
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