Structural and Functional Responses of Soil Microbial Communities to Biodegradable Plastic Film Mulching in Two Agroecosystems

Abstract

18Polyethylene (PE) plastic mulch films are used globally in crop production but incur considerable 19 disposal and environmental pollution issues. Biodegradable plastic mulch films (BDMs), an 20 alternative to PE-based films, are designed to be tilled into the soil where they are expected to be 21 mineralized to carbon dioxide, water and microbial biomass. However inadequate research 22 regarding the impacts of repeated incorporation of BDMs on soil microbial communities has partly 23 contributed to limited adoption of BDMs. In this study, we evaluated the effects of BDM 24 incorporation on soil microbial community structure and function over two years in two 25 geographical locations: Knoxville, TN, and in Mount Vernon, WA. Treatments included four 26 plastic BDMs, a completely biodegradable cellulose mulch, a non-biodegradable PE mulch and a 27 no mulch plot. Bacterial community structure determined using 16S rRNA amplicon sequencing 28 revealed significant differences by location and season. Differences in bacterial communities by 29 mulch treatment were not significant for any season in either location, except for Fall 2015 in WA 30 where differences were observed between BDMs and no-mulch plots. Extracellular enzyme rate 31 assays were used to characterize communities functionally, revealing significant differences by 32 location and sampling season in both TN and WA but minimal differences between BDMs and PE 33 treatments. Limited effects of BDM incorporation on soil bacterial community structure and soil 34 enzyme activities when compared to PE suggest that BDMs have comparable influences on soil 35 microbial communities, and therefore could be considered an alternative to PE. 36 Importance 37 Plastic film mulches increase crop yields and improve fruit quality. Most plastic mulches are made 38 of polyethylene (PE), which is poorly degradable, resulting in undesirable end-of-life outcomes. 39 Biodegradable mulches (BDMs) may be a sustainable alternative to PE. BDMs are made of 40 3 polymers which can be degraded by soil microbial enzymes, and are meant to be tilled into soil 41 after use. However, uncertainty about impacts of tilled-in BDMs on soil health has restricted 42 adoption of BDMs. Our previous research showed BDMs did not have a major effect on a wide 43 range of soil quality indicators (Sintim et al. 2019); here we focus on soil microbial communities, 44 showing that BDMs do not have detectable effects on soil microbial communities and their 45 functions, at least over the short term. This informs growers and regulators about use of BDMs in 46 crop production, paving a way for an agricultural practice that reduces environmental plastic 47 pollution.48

Preliminary Findings of Polypropylene Carbonate (PPC) Plastic Film Mulching Effects on the Soil Microbial Community

“…Therefore, we believe that the short-term one-year PPC film mulching has little effect on the overall soil microorganisms. The study by Sreejata et al also did not detect any significant effect of plastic mulches on bacterial community structure, richness, or diversity [41]. We explored the effect of the PPC film mulching on the microbial community in the overall large space of the soil, rather than the microorganisms in the soil next to the plastic film, ignoring the microbial changes on the local spatial scale; thus, we believe that mulching has little effect on the overall system of soil microorganisms.…”

Comparative Analysis of the Effects of Plastic Mulch Films on Soil Nutrient, Yields and Soil Microbiome in Three Vegetable Fields

“…Basidiomycota also has the ability to break down lignocellulose, but it is an oligotrophic microorganism and is adapted to relatively poor soil [52], so the abundance was inversely proportional to C/N [53]. However, the impact of BDMs on fungi is affected by the environment, soil type and soil management [10,54].…”