Iron oxides promote physicochemical stabilization of carbon despite enhancing microbial activity in the rice rhizosphere

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Sun, H
Ma, X
Van Zwieten, L
Luo, Y
Brown, RW
Guggenberger, G
Tang, S
Kuzyakov, Y
Jeewani, PH
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2025
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Abstract

Rice rhizosphere soil is a hotspot of microbial activity and a complex interplay between soil abiotic properties, microbial community and organic carbon (C). The iron (Fe) plaque formation in the rice rhizosphere promotes Fe-bound organic C formation and increases microbial activity. Yet, the overall impact of Fe on C storage via physicochemical stabilization and microbial mineralization of rhizodeposits (rhizo-C) and soil organic C (SOC) in the rice rhizosphere remain unclear. We conducted a microcosm experiment using 13C-CO2 pulse labeling to grow rice (Oryza sativa L.) with four levels of α-FeOOH addition (Control, Fe-10 %, Fe-20 %, Fe-40 % w/w of α-FeOOH per total Fe in soil). This study aimed to evaluate the impact of Fe oxides on rhizo-C mineralization, the rhizosphere priming effect, and Fe-OM formation. Microbial community composition and localization of enzyme activities were also quantified through 16S rRNA sequencing and zymography. The hotspot area, as being indicated by zymography, increased by 20-50% in the presence of Fe compared to the soil without Fe addition. Despite being a hotspot, strong coprecipitation of Fe-OM in the rhizosphere promoted C immobilisation. Fe-20 % and Fe-40 % resulted in a 41 % and 33 % decrease of rhizodeposits derived 13C-CO2 emission and increased 13C stabilization mainly in 0.25–2 mm soil aggregates due to coprecipitation and aggregate formation with α-FeOOH. Moreover, Fe addition led to a dominance of Fe-oxidizing bacteria genera such as Pseudomonas, which fostered coprecipitation of Fe-OM formation. We highlight larger physicochemical stabilization of organic C by α-FeOOH addition despite raised hotspot area of microbial activity in the rice rhizosphere.

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Science of the Total Environment

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958

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Soil sciences

Agricultural biotechnology

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Sun, H; Ma, X; Van Zwieten, L; Luo, Y; Brown, RW; Guggenberger, G; Tang, S; Kuzyakov, Y; Jeewani, PH, Iron oxides promote physicochemical stabilization of carbon despite enhancing microbial activity in the rice rhizosphere, Science of the Total Environment, 2025, 958, pp. 178019

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