Living in the plastic age - Different short-term microbial response to microplastics addition to arable soils with contrasting soil organic matter content and farm management legacy

Abstract

Microplastics (MPs) are an emerging pollutant found in many ecosystems including soils, where they may become toxic to organisms or alter their habitat. However, little is known about the influence of MPs on soil microorganisms and processes vital to ecosystem functioning in different soils. Therefore, our objective was to investigate the short-term effects of MPs pollution on soil microorganisms in two agricultural soils with contrasting soil organic matter content and microbial biomass as caused by farm management history (organic and conventional). Soils were amended with two kinds of raw MPs particles, low-density polyethylene (LDPE) and polypropylene (PP) in the size range of 200-630 μm at a rate of 1% w/w and incubated for 28 days. During incubation, microbial respiration was determined. After incubation, the microbial biomass carbon (C) and nitrogen (N), gene copy numbers of archaea, bacteria and fungi were quantified and extractions performed to gauge effects on C and N mineralisation. The results of this study showed no major detrimental effects of MPs on microbial activity. However, in particular PP reduced microbial biomass in both soils, with a stronger decline in the organic soil, showing lower resistance to MPs. Nevertheless, mineralisation processes remained on the same level, showing functional resistance of the microbial community to MPs addition in both soils. The microbial community composition was not significantly altered by MPs addition, even though fungi tended to decrease in the organic soil. Overall, management legacy had a stronger effect on soil microorganisms, with higher microbial biomass and activity in the organic soil. While this study does not answer whether MPs pollution has a negative impact on soil microorganisms, it highlights the need to consider potential interactive effects of environmental factors, land use and management with MPs on soil microbial communities and their functions.

Keywords: Fungi-bacteria; Microplastics; Organic farming; Soil microbial activity; Soil microbial biomass.