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Polyethylene microplastics–biochar coexistence induces a positive priming effect on native soil organic carbon mineralization while enhancing glucose retention
Summary
Microplastics are everywhere in soil now, and this study looked at how they interact with biochar (a charcoal-like soil additive used to boost soil health and lock away carbon). The surprising finding: whether this combo helps or hurts soil's ability to store carbon depends heavily on how the biochar was made, specifically the temperature used to produce it, showing that "adding biochar to fix microplastic-contaminated soil" isn't a one-size-fits-all solution. This matters because healthy soil that stores carbon well supports the food system we all depend on, and getting the biochar recipe wrong could backfire as microplastic p
The impacts of microplastics (MPs) and biochar on root exudate-induced priming effect on native soil organic carbon mineralization (PE-NSOC) and on root exudate mineralization remain poorly understood. Here, C stable isotope labeling combined with biochar-specific biomarkers (benzene polycarboxylic acids, BPCAs) was used to partition CO emissions from NSOC, glucose (root exudate representative), and biochar. Polyethylene MPs (PE-MPs) exerted limited effects on glucose-induced PE-NSOC, which remained negative, similar to glucose alone. Conversely, corn straw biochar (CSB) markedly reversed PE-NSOC from negative to positive, likely through early-stage nutrient limitation followed by late-stage microbial stimulation. Importantly, pyrolysis temperature dictated the direction of MP-biochar interactions: PE-MPs further enhanced positive PE-NSOC induced by low-temperature CSB, but weakened it when combined with high-temperature CSB. All treatments suppressed glucose mineralization, with the strongest inhibition observed for PE-MPs combined with high-temperature CSB, probably due to the enhanced adsorption, bacterial diversity, and nitrogen-acquisition enzyme activities (e.g., leucine aminopeptidase). Carbon balance analysis revealed net SOC gains in most treatments, except PE-MPs combined with low-temperature CSB, with the greatest increase occurring under glucose plus PE-MPs. These findings highlight the importance of biochar pyrolysis temperature in regulating MP-biochar interactions and provide guidance for biochar-based carbon management in MP-contaminated soils.