Native soil fungi associated with compostable plastics in three contrasting agricultural settings

Abstract

Plastics are used widely as agricultural mulches to suppress weeds and retain soil moisture. Disposal of conventional plastic mulches requires physical removal for disposal in a landfill or incineration. Biodegradable plastic mulches that could be tilled into the soil at the end of a growing season represent an attractive alternative to conventional plastic mulches. In this study, three commercially available mulches labeled as "biodegradable" and one experimental, potentially biodegradable mulch were used during a tomato growing season, and then buried in field soil at three locations for approximately 6 months, as would occur typically in an agricultural setting. Degradation after 6 months in soil was minimal for all but the cellulosic mulch. After removal of mulches from soil, fungi were isolated from the mulch surfaces and tested for their ability to colonize and degrade the same mulches in pure culture. The majority of culturable soil fungi that colonized biodegradable mulches were within the family Trichocomaceae (which includes beneficial, pathogenic, and mycotoxigenic species of Aspergillus and Penicillium). These isolates were phylogenetically similar to fungi previously reported to degrade both conventional and biodegradable plastics. Under pure culture conditions, only a subset of fungal isolates achieved detectable mulch degradation. No isolate substantially degraded any mulch. Additionally, DNA was extracted from bulk soil surrounding buried mulches and ribosomal DNA was used to assess the soil microbial community. Soil microbial community structure was significantly affected by geographical location, but not by mulch treatments.

Effects of biodegradable plastic film mulching on soil microbial communities in two agroecosystems

“…Here we show that any local effects of mulch films are not detectable at a field scale, at least over a two-year period. We did note significant differences in soil bacterial composition by location and season, which has been observed in other studies (Li et al, 2014b;Moore-Kucera et al, 2014). In our study, mulch effects were minimal compared to other drivers of community structure variation.…”

“…Some of the agronomic benefits of using plastic mulch films include reduction of weed pressure (Martín-Closas, Costa & Pelacho, 2017), conservation of soil moisture (Kader et al, 2017;Shahi et al, 2017), and moderation of soil temperature. Low density polyethylene (PE) has been the favored polymer for mulch films due to its many attractive properties such as low cost, easy processability, high durability and flexibility (Bandopadhyay et al, 2018; have analyzed impacts of BDMs on soil microbial communities using phospholipid fatty acid (PLFA) profiling (Li et al, 2014b) and pyrosequencing (Moore-Kucera et al, 2014) methods. However, these studies did not use PE as a negative control so direct effects of BDMs on soil microbial community structure and function remain uncertain.…”

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

“…We did note significant differences in soil bacterial composition by location and season, which has been observed in other studies (29, 30), confirming that mulch effects are minimal compared to other drivers of community structure variation. It is well accepted that local soil conditions such as temperature, moisture and pH play a pivotal role in shaping microbial communities (30, 44, 45).…”

“…Previous studies have also demonstrated increased fungal abundances in soil because of BDM incorporation (29, 41, 49, 50). Fungi have been observed to be important colonizers and degraders of BDMs (30, 40, 41). Tilled into soil, BDMs are a very small input of carbon when taking into account the volume of soil into which they are incorporated (5).…”

“…These answers are critical if widespread use of BDMs is to be advocated. Previous studies have analyzed impacts of BDMs on soil microbial communities using PLFA profiling (29) and pyrosequencing (30) methods.…”