With the increasing of human population, the yield and quality of grain have become the most serious problems. The emergence of plastic film mulching (PFM) has solved a problem, as precipitation and other water resources are used more efficiently to attain the required food production. PFM is primarily used to protect shoots and seedlings and maintain or increase soil humidity and temperature through insulation and evaporation prevention (Steinmetz et al., 2016). Furthermore, PFM may increase yields; extend the growing season; conserve soil moisture and water-use efficiency; increase fertilizer use efficiency; prevent soil erosion with weed growth; and reduce weed pressure, as well as consequently reduce herbicide and fertilizer use. In recent years, the usage of PFM has been increasing in worldwide (Cuello et al., 2015). For example, in China, about 14.7 × 105 tons PFM have been used on crops (Gao et al., 2019), most of which is distributed in 19.8 million hectares of agricultural land, while in Europe, areas of PMF cover approximately 162,000 ha (Briassoulis and Dejean, 2010), and in the U.S.A, only in vegetable production, more than 130,000 metric tons of plastics are used (LI et al., 2014). However, PFM have improved crop yield significantly and solved greatly the food crisis, but also results in a series of issues as well. For example, residues of plastics in the soil have become one of the major environmental pollution sources. The residues include microplastics, phthalates, and agrochemicals, all of which have been found to lead to substantial amounts of plastic waste residue accumulation and may possibly liberate toxic additives into the soil (Steinmetz et al., 2016) and promote soil water repellency and soil degradation. At present, the residues from PFM in the soil are also a serious problem, and burning and disposing of PFM in open fields or landfills are common. Although PFM is legal, it has been repeatedly banned due to its simplicity and low operating cost, which has a huge negative impact on product quality, human health and the environment. Therefore, whether BDFs can be used as an alternative to NBDF has been a hot topic.
Biodegradable plastic mulch (BPM), synthesized first in the mid-1970s (Briassoulis and Dejean, 2010; LI et al., 2014), consists of either BDFs plastics (i.e., plastics produced from fossil materials) or biobased plastics (i.e., plastics synthesized from biomass or renewable resources) (Tokiwa et al., 2009) and mainly indicate the instead of traditional geoponic PFM, which can't be recovered from the soil for financial or technical reasons. BPM primarily consists of biobased plastics that will biodegrade after the end of their effective process without leaving toxic and polluting remains in the soil (Li et al. 2014). The advantages of BDFs are as follows: improved tensile strength, flexibility, and controllability of rupture and degradation; pollution free; enhanced ability to increase the soil temperature and preserve the soil moisture and satisfy the demand of crop production with mulching (Yan et al., 2016). However, some shortcomings of BDFs are also exposed as the service time increases. For instance, there is perceived uncertainty about the weak market transparency, product properties, a lack of uniformity in the product, and a discouraging cost of biodegradable plastic mulch compared to conventional mulch in certain applications (Briassoulis and Dejean 2010). For some reason, bewilderment still existence regarding the capability of these materials under real soil conditions. Studies show the incomplete breakdown of BDFs could lead to an accumulation of plastic fragments and particulates in soils (Sintim and Flury, 2017). Therefore, whether BDFs may become a desirable alternative to traditional PFM with solve agricultural plastic problems remains a question.
Microbes are an important part of soil, and their diversity and function, i.e., their abundance and activity, as well as the community structure (Puglisi et al., 2012), may act as a prime indicator of soil fertility and quality. Microbes are sensitive to soil contaminants, their activity and composition are the primary biological indicators of alters in the soil environment, as they play a key role in carbon, phosphorus, nitrogen, and potassium cycling in the soil (Qian et al., 2018). Recent reports have found that PFM can also influence the activities and composition of soil microbes (Cook et al., 2006; Subrahmaniyan et al., 2006). Some bacterial strains in the soil have been found to be involved in microplastic degradation. However, biodegradable plastic mulches are now widely used and can be amalgamated into the soil at the end of the crop season and decomposed by microbes, such as bacteria, fungi and algae, eventually released into the soil in the form of CO2 and H2O (Ashley and Jo, 2012). Thus, the abundance and activity of soil microbes may be change along with the disposal of BDFs.
In this study, we evaluated the effects on microbes diversity, abundance in soils mulched by three potentially biodegradable films (BDFs: BDF1, BDF2, BDF3) and one nonbiodegradable films (NBDF, also named polyethylene film), respectively. We also quantified the abundance of some functional microbes that can improve soil fertility as well as soil properties, or accelerate degradation of the BDFs. Our results highlight the effect of the BDFs mulch on soil microbes diversity that might be involved in the degradation of BDFs.