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Background and purpose <p>The coexistence of microplastics and heavy metals in agricultural soils poses a significant threat to ecosystem health and food security. This study investigated the combined effects of polystyrene microplastics (PS-MPs) of different sizes and heavy metals (HMs) on soil health, the bacterial community, and the growth of spring onions (<i>Allium fistulosum)</i>. The main research question was how smaller PS-MPs, in conjunction with HMs, influenced soil physicochemical properties, shifted bacterial diversity and composition, and induced physiological stress and growth inhibition in <i>Allium fistulosum</i>.</p> Materials and methods <p>A greenhouse pot experiment was conducted using HM-contaminated soil from Tongling City, and spring onions were cultivated in soil amended with three sizes of PS-MPs (13&#xa0;μm, 50&#xa0;μm, 106&#xa0;μm). After 20 and 40 days of seedling growth, the rhizosphere and the bulk soil were sampled to analyze soil physicochemical properties, plant biometric and biochemical stress markers (antioxidant enzymes, electrolytic leakage), and bacterial diversity, composition via high-throughput 16&#xa0;S rRNA sequencing. Analysis of variance (ANOVA) was performed to determine significant differences between treatments.</p> Results and discussion <p>Our results demonstrated a clear size-dependent toxicity. The smallest PS-MPs (13&#xa0;μm) exerted the most profound effects, significantly increasing pH, organic matter, electrical conductivity, and specific HM availability (Zn, Cu, Cd), while reducing nitrogen compounds. Concomitantly, plant growth was severely inhibited, and a significant rise in electrolytic leakage, antioxidant activity confirmed oxidative stress. Crucially, the soil microbiome was drastically altered; saprotrophs declined, while plant and animal pathogens were significantly enriched, with a 27% increase in pathogenic abundance in the rhizosphere of the 13&#xa0;μm MP treatment. The results suggest that smaller MPs act as a stronger vector for HM toxicity and create a favorable niche for pathogens, compounding stress on plants and disrupting soil ecosystem functions.</p> Conclusions <p>Our results demonstrate a greater aggravation of stress in a co-contaminated system, significantly deteriorating soil health, altering microbial communities to favor pathogens, and severely inhibiting plant growth. Our findings underscore that microplastic size is a critical factor in ecological risk assessment for co-contaminated soils. Future research must focus on the long-term ecological consequences of these interactions to develop effective remediation strategies for co-contaminated agricultural soils.</p>

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Size-dependent impacts of polystyrene microplastics and heavy metals on soil microbiomes and spring onion (Allium fistulosum) health

  • 期刊论文

  • 发表日期：

    2026年4月17日

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  • Jazbia Shirin,
  • Nazish Jabeen Abbasi,
  • Syeda Anber Zahra,
  • Azhar Hussain Shah,
  • Qingye Sun,
  • Qiyong Xu

摘要

Background and purpose

The coexistence of microplastics and heavy metals in agricultural soils poses a significant threat to ecosystem health and food security. This study investigated the combined effects of polystyrene microplastics (PS-MPs) of different sizes and heavy metals (HMs) on soil health, the bacterial community, and the growth of spring onions (Allium fistulosum). The main research question was how smaller PS-MPs, in conjunction with HMs, influenced soil physicochemical properties, shifted bacterial diversity and composition, and induced physiological stress and growth inhibition in Allium fistulosum.

Materials and methods

A greenhouse pot experiment was conducted using HM-contaminated soil from Tongling City, and spring onions were cultivated in soil amended with three sizes of PS-MPs (13 μm, 50 μm, 106 μm). After 20 and 40 days of seedling growth, the rhizosphere and the bulk soil were sampled to analyze soil physicochemical properties, plant biometric and biochemical stress markers (antioxidant enzymes, electrolytic leakage), and bacterial diversity, composition via high-throughput 16 S rRNA sequencing. Analysis of variance (ANOVA) was performed to determine significant differences between treatments.

Results and discussion

Our results demonstrated a clear size-dependent toxicity. The smallest PS-MPs (13 μm) exerted the most profound effects, significantly increasing pH, organic matter, electrical conductivity, and specific HM availability (Zn, Cu, Cd), while reducing nitrogen compounds. Concomitantly, plant growth was severely inhibited, and a significant rise in electrolytic leakage, antioxidant activity confirmed oxidative stress. Crucially, the soil microbiome was drastically altered; saprotrophs declined, while plant and animal pathogens were significantly enriched, with a 27% increase in pathogenic abundance in the rhizosphere of the 13 μm MP treatment. The results suggest that smaller MPs act as a stronger vector for HM toxicity and create a favorable niche for pathogens, compounding stress on plants and disrupting soil ecosystem functions.

Conclusions

Our results demonstrate a greater aggravation of stress in a co-contaminated system, significantly deteriorating soil health, altering microbial communities to favor pathogens, and severely inhibiting plant growth. Our findings underscore that microplastic size is a critical factor in ecological risk assessment for co-contaminated soils. Future research must focus on the long-term ecological consequences of these interactions to develop effective remediation strategies for co-contaminated agricultural soils.