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Macroplastics in soybean cultivation: Neutral on plant growth but disruptive to nitrogen-fixing microbiome
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Researchers studied how larger plastic debris (over 2 centimeters) in agricultural soil affects soybean growth and the nitrogen cycle over a 71-day experiment. While the macroplastics did not visibly affect plant growth, they significantly disrupted nitrogen-fixing bacterial communities and altered soil nitrogen chemistry. The study suggests that even when crop yields appear unaffected, plastic contamination in farmland may be quietly undermining the beneficial soil microorganisms that plants depend on.
Macroplastics are an emerging yet underexplored pollutant in agricultural soils, with the potential to disrupt nitrogen (N) cycling through physical interference and microbial community shifts. While extensive studies have focused on microplastics, the effects of larger plastic debris (>2 cm) on soil-plant systems in legume cropping systems remain poorly understood. We conducted a 71-d mesocosm study utilizing N isotopic tracing and metagenomic sequencing to demonstrate how macroplastics influence soybean growth and soil-soybean continuum N cycling. Soybean growth was not affected under macroplastics exposure (up to 200 kg ha⁻). However, macroplastics increased soil NO₃⁻ and NH₄⁺ concentrations, and elevated urease and ammonia monooxygenase activities, suggesting enhanced N availability. Paradoxically, macroplastics significantly disrupted the N-fixing microbial community, reducing the abundance of key bacteria such as Azorhizobium and Bradyrhizobium. Nitrogen fixation pathways (in log10-transformed TPM+1) were markedly suppressed in soils treated with 200 kg ha⁻¹ macroplastics compared to untreated soils (p < 0.001). Our findings highlight the potential risks of macroplastics posing to N cycling and microbial health in agricultural soils. This study addresses a critical knowledge gap by shifting the focus from micro- to macroplastic impacts on biogeochemical cycling.
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Sub-micron microplastics affect nitrogen cycling by altering microbial abundance and activities in a soil-legume system
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Researchers found that very small (sub-micron) polyethylene and polypropylene microplastics in soil significantly altered nitrogen cycling by changing the abundance and activity of bacteria around soybean roots. While the microplastics did not affect plant growth directly, they increased nitrogen uptake and shifted the balance of nitrogen-processing bacteria. These hidden changes to soil chemistry could have long-term effects on agricultural productivity and the nutritional quality of crops.
Effects of microplastic contamination on soil nitrogen and its bioavailability in soybean-maize rotation system
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Researchers conducting a field experiment found that microplastics in agricultural soil disrupt the nitrogen cycle in a soybean-maize rotation system, inhibiting the natural nitrogen fixation that legumes provide and increasing the conversion of ammonium to nitrate — a form more prone to leaching away — raising concerns for long-term soil fertility.
Microplastics affect the nitrogen nutrition status of soybean by altering the nitrogen cycle in the rhizosphere soil
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Researchers investigated how three types of microplastics — polystyrene, polyethylene, and polyvinyl chloride — affect soybean growth by altering nitrogen cycling in the root-zone soil. They found that polyethylene and polystyrene promoted nitrogen availability and soybean growth, while polyvinyl chloride disrupted the nitrogen cycle, reduced beneficial soil microorganisms, and inhibited plant growth. The study suggests that different types of microplastics can have opposing effects on crop nutrition through their impact on soil microbial communities.
Microplastics affect soybean rhizosphere microbial composition and function during vegetative and reproductive stages
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Researchers conducted a 70-day greenhouse experiment to evaluate how four types of microplastics affect soybean rhizosphere bacterial communities in two soil types. The study found that polyamide microplastics consistently altered bacterial diversity and nitrogen cycling functions, while other plastic types had shorter-term effects, suggesting that different microplastics pose varying risks to agricultural soil microbial ecosystems.
Deciphering the response of nodule bacteriome homeostasis in the bulk soil-rhizosphere-root-nodule ecosystem to soil microplastic pollution
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Researchers examined how polyethylene microplastic contamination in soil affects the bacterial communities associated with legume plant root nodules. They found that microplastic treatments accelerated nodule formation but disrupted the balance of beneficial nitrogen-fixing bacteria in the nodules. The study suggests that soil microplastic pollution may interfere with the symbiotic relationship between legume crops and their nitrogen-fixing bacterial partners.
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