Soil constituents mediate the effects of microplastics from biodegradable mulch on soil biogeochemical properties

Terrestrial microplastics are increasing in abundance and are an emerging contaminant of concern, particularly in agroecosystems where plastic mulch use and subsequent soil contamination are prevalent. In response to this issue, biodegradable plastic mulches (BDMs) have been promoted as sustainable alternatives to conventional fossil fuel-based mulches. BDMs are designed to be tilled back into the soil where they are expected to degrade; however, this has proven to be dependent on soil type, climate, and polymeric composition, thus inconsistent, potentially leading to the accumulation of biodegradable microplastics (BDMPs) in soil that can have adverse effects like those of microplastics generated from conventional, non-biodegradable mulches. To evaluate the environmental impact of this conventional plastic mulch alternative, this 2-month incubation study explored the effects of BDMPs derived from PBAT-based BDM on a suite of soil health indicators, including physical soil properties, extractable nutrients, and microbial activities. Using laboratory-prepared soils amended with a BDMP concentration of 1 % (w/w), we assessed how clay mineralogy and organic matter content influence soil–BDMP interactions under controlled conditions. Our results suggest there is a significant effect of BDMPs on soil moisture and nutrient cycling with a potential negative priming effect, particularly in soils where organic matter is limited. While BDMP presence altered soil C pools, a qualitative analysis suggests the BDMPs remained largely undegraded by the end of the incubation. Additionally, clay mineralogy significantly mediated the BDMP effects on physical soil properties. These findings suggest that BDMPs have the potential to influence soil properties and functions relative to baseline soil characteristics, underscoring the need for further research to fully understand their environmental implications. • Artificial soils varied by clay mineralogy and organic matter in an incubation. • Microplastics from BDM affected biotic and abiotic soil response variables. • Direction and magnitude of effects depended on innate soil characteristics. • Soil nutrient limitation exacerbated the effects of biodegradable microplastics.