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Published on: February 15, 2021
Rhizosphere phosphorus and iron cycling accelerates manganese phytoextraction by Polygonum lapathifolium
Chijian Tang1, Cuiping Wan1, Jianing Gan1
1Guangxi Key Laboratory of Environmental Processes and Remediation in Ecologically Fragile Regions, Guangxi Normal University, Guilin 541004, China; University Engineering Research Center of Green Remediation and Low Carbon Development for Lijiang River Basin, Guangxi Normal University, Guilin 541004, China.
Abstract:
Manganese (Mn) contamination in mining soils poses persistent ecological risks due to its high mobility and potential accumulation in plants. Although exogenous microbial inoculation is increasingly used to improve phytoremediation, the mechanisms by which it regulates rhizosphere phosphorus (P) and iron (Fe) cycling, and thereby influences Mn bioavailability, remain poorly understood. We hypothesized that Enterobacter sp. inoculation would enhance Mn phytoextraction by stimulating rhizosphere P activation and Fe speciation transformation, thereby promoting nutrient acquisition and Mn mobilization. To test this hypothesis, we investigated the effects of Enterobacter sp. inoculation on rhizosphere P/Fe fractions, functional genes, and Mn phytoextraction. Enterobacter sp. significantly decreased rhizosphere soil pH and enhanced P-releasing enzyme activities, increasing available P by 26.7% under the C1.0 (3.8 ×107 CFU·g-1 (soil)) treatment compared with the control (p < 0.05). Concurrently, Fe(II) and amorphous Fe increased by 11.9% and 15.1%, respectively (p < 0.05), indicating enhanced Fe transformation in the rhizosphere. These shifts facilitated plant P and Fe acquisition, promoted biomass production, enhanced Mn phytoextraction in Polygonum lapathifolium L. by strengthening rhizosphere redox conditions and mineral interfacial processes. Metagenomic analysis revealed that Enterobacter sp. inoculation increased the functional potential of genes related to P activation (e.g., gcd, phnP) and Fe biosynthesis/uptake (e.g., hemH, pchB), mainly associated with Pseudomonadota and Actinomycetota. Partial least squares path modeling further confirmed positive associations among P/Fe cycling genes, rhizosphere P/Fe fractions, enzymatic activities, and plant growth. Overall, microbial inoculation enhanced Mn phytoremediation by coordinating rhizosphere nutrient cycling processes, providing a promising strategy for the remediation of HMs-contaminated mining soils.
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