Microbial communities in soil play important roles for plant health, growth and stress resilience. Yet, soil pollution can challenge microbial activity and thus lead to decreased crop yield affecting global food production. Especially the effects of microplastics on the function of soil microbes are underexplored at this point, which is the focus of a recent study in FEMS Microbiology Ecology. In a #BehindThePaper interview, Yueling Qi talks about the impact microplastics have on soil suppressiveness and why we need to pay more attention to how resistant soils are to pathogens. #FEMSmicroBlog
How are environmental plastic residues related to soil suppressiveness?
To improve the microclimate of the soil and water use efficiency, many farmers cover their farmlands with plastic films. This technique is called plastic mulching and unfortunately, the film residues can remain in the soil, where it leads to severe plastic pollutions. And especially regions with intensive use of plastic mulching have serious environmental problems.
On the one hand, previous studies showed that plastic residues impact the soil microbiome, for instance they affect the diversity and composition of rhizosphere microbial communities. On the other hand, the soil microbiome and its microbial activity is closely related to soil suppressiveness. This is a function of the soil to withstand plant pathogens so that plants in this soil are protected from disease and infection. Therefore, we hypothesised that plastic residues could affect soil suppressiveness by impacting the soil microbiome.
Why is it important to study the impact of plastic residues on the soil microbiome and suppressiveness?
Firstly, plastic pollution — especially microplastic pollution — in agriculture is an increasingly deteriorating environmental issue! It is estimated that the annual plastic release to land was 4 to 23 times higher than what was released to oceans. Microplastics can enter farmland via multiple pathways for instance, land application of sludge, irrigation with wastewater, plastic mulching, landfills, littering and atmospheric deposition etc.
Because of all these entry points, the mass of microplastics currently stored in agricultural soils alone could be more than the microplastics stored in oceanic basins. However, most studies on microplastics have focused on aquatic ecosystems. Due to these most vulnerable environmental compartments to plastic pollution, studies focusing on plastic residues in agricultural soil are urgently needed.
Secondly, disease-suppressive soils can protect plants from root pathogens despite the presence of favourable conditions for disease development. Enhancing soil suppressiveness is of great agronomic interest and has the potential to resist soil-borne plant pathogens in a sustainable way. Therefore, it is important to investigate the impact of plastic residues on soil suppressiveness to understand how well soils protect plants from pathogens and disease.
How do plastic residues in soil affect the microbiome and soil suppressiveness?
To prove our hypothesis, we used wheat as a model host plant along with an agricultural soil that is suppressive to a common fungal pathogen (Fusarium culmorum). We conducted a pot experiment to test if the addition of plastic residues to the soil affect soil suppressiveness. In this pot experiment, the presence of plastic mulch film residues did not affect the disease infection level of wheat in the suppressive soil. Yet, the plant biomass decreased and the plant nutrient content was affected by the presence of plastic residues.
In our study, we found that microbial communities could attach to the plastic residues as biofilms forming the so-called ‘plastisphere’. Since they attracted and possibly activated specific microorganisms, we suggested plastic residues to influence the soil microbiome as well.
However, we found that the bacterial and fungal communities in the rhizosphere were not changed by the presence of plastic residues. The reason for this unexpected observation could be that we performed only a short-term experiment (two weeks for activation and three weeks for infection). Therefore, it is plausible that in the long term, residues of microplastics in soil may cause stronger and more significant effects. All in all, this initial research brings new insights and raises questions for further studies of microplastics in agroecosystems. It is of great agronomic interest to further explore the effects of plastic residues on soil suppressiveness and other soil functions.
- Read the paper “Plastic mulch film residues in agriculture: impact on soil suppressiveness, plant growth and microbial communities” by Qi et al. (2022) in FEMS Microbiology Ecology.
Yueling Qi is a lecturer at the School of Resources and Environmental Engineering, Anhui University in China. She did her PhD at Wageningen University and the Netherlands Institute of Ecology (NIOO-KNAW) from 2016 to 2020. Her PhD research focused on the ecological impacts of plastic mulch film residues on agroecosystem and soil-plant systems. She went back to her homeland China by the end of 2020 after finishing her PhD study in the Netherlands, and she is determined to continue working on plastic pollution in agriculture being a university teacher.
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