Bioplastic (PHBV) addition to soil alters microbial community structure and negatively affects plant-microbial metabolic functioning in maize

Abstract

Microplastic contamination poses a significant threat to agroecosystem functioning, provoking a move away from the use of conventional oil-based plastics in agriculture, to biodegradable alternatives that may be degraded over a shorter timescale. The impact of these bioplastics on plant and soil health, however, has received relatively little attention. Here, we investigated the effect of soil loading (0.01%, 0.1%, 1% and 10%) of biobased microplastic poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) on soil and plant ( Zea mays L.) health and function. We showed that PHBV caused a dose-dependent reduction in plant growth and foliar nitrogen (N) content while untargeted metabolite analysis revealed significant shifts in foliar metabolic function. These results were also reflected in soil, where PHBV led to reduced plant availability of both ammonium and nitrate. Soil 14 C-isotope tracing and 16 S metabarcoding revealed that PHBV supressed microbial activity, reduced bacterial diversity and shifted microbial community structure, inducing a major shift in soil metabolic pathways, and thus functioning. Overall, our data suggests that the bioplastic PHBV is not environmentally benign and that contamination levels as low as 0.01% (0.01 mg kg -1 ) can induce significant short-term changes in both plant and soil microbial functioning, with potential implications for long term agroecosystem health. • Effect of biopolymer PHBV microplastic on soil and plant health was investigated • PHBV addition caused a dose-dependent negative effect on soil and plant health • PHBV addition altered foliar metabolism and reduced plant growth and foliar N • PHBV reduced soil microbial activity and changed the bacterial community structure • Bioplastics may not be environmentally benign