LDPE and biodegradable PLA-PBAT plastics differentially affect plant-soil nitrogen partitioning and dynamics in a Hordeum vulgare mesocosm

• Published in: Journal of hazardous materials 2023-04, Vol.447, p.130825-130825, Article 130825
• Main Authors: Reay, Michaela K., Greenfield, Lucy M., Graf, Martine, Lloyd, Charlotte E.M., Evershed, Richard P., Chadwick, Dave R., Jones, Davey L.
• Format: Article
• Language: English
• Subjects: 15N stable isotope probing; Amino acids; Biodegradable Plastics; Hordeum; Macroplastic; Microplastic; Microplastics; Nitrogen; Plants; Plastics; Polyesters; Polyethylene; Risk threshold; Soil; Soil Pollutants
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2023.130825

Micro and macroplastics are emerging contaminants in agricultural settings, yet their impact on nitrogen (N) cycling and partitioning in plant-soil-microbial systems is poorly understood. In this mesocosm-scale study, spring barley (Hordeum vulgare L.) was exposed to macro or microplastic produced from low density polyethylene (LDPE) or biodegradable plastic at concentrations equivalent to 1, 10 and 20 years of plastic mulch film use. Partitioning of 15N-labelled fertiliser into plant biomass, soil and leachate yielded a partial mass balance. Soil N partitioning was probed via compound-specific 15N-stable isotope analyses of soil microbial protein. Concentration-dependent decreases in plant 15N uptake occurred with increased leached nitrogen for LDPE microplastic. Assimilation into soil microbial protein was higher for biodegradable plastics, which we associate with early-stage biodegradable plastic degradation. Partitioning of 15N into inorganic soil N pools was affected by LDPE size, with lower assimilation into the microbial protein pool. While microplastics and macroplastics altered soil N cycling, the limited impacts on plant health indicated the threshold for negative effects was not reached at agriculturally relevant concentrations. This study highlights the difference between conventional and biodegradable plastics, and emphasises that the interplay of micro and macroplastics on soil N cycling must be considered in future studies. [Display omitted] •Barley was exposed to biodegradable and LDPE macro and microplastic.•15N-tracing indicated LDPE microplastic reduced plant 15N uptake due to N losses.•LDPE plastics altered partitioning of 15N within soil N pools.•Biodegradable macro and micro plastic increased microbial N uptake.•Biodegradable and LDPE plastics had differing impacts on plant-soil N partitioning.