Microplastic occurrence and effects on soil fungi and processes along land use gradients

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We live in a heavily plastic-influenced world, as plastic is ubiquitous in our daily lives. As a consequence, plastic has been found in a wide range of environmental compartments, predominantly as microplastics, that is plastic pieces < 5 mm. After initially having been studied in marine and aquatic systems only, soils have come into focus much more recently in terms of microplastic, with data beginning to show that this may be a rather widespread contaminant of soils, with potential consequences for soil physical, chemical and biological parameters. Given the range of input pathways, which include plastic trash, compost, aerial deposition and roads, there is good reason to assume that microplastics will be present in Biodiversity Exploratory soils. Our research has two main goals: First, we want to know if microplastics (presence and/ or type) can track land use intensity, thus serving as a signature of human intervention and activity. To address this, we will sample soils from all 150 EPs in grassland and assay them for microplastic presence, type and composition using state-of-the-art methods of extraction and identification (Fourier-transform infrared spectroscopy microscopy). We can then link these data to land use intensity (LUI) or its components, as well as to general soil properties available at the EP-level.Second, we want to test the effects of experimental microplastic addition in the field, along the land use gradient. We will approach this with the deployment and re-sampling (after 1 yr) of small mesh bags containing microplastic- contaminated soil, which will be buried in all VPs in grassland (containing the soil from each VP). The microplastic we will use for this is polyester fibers, which we have previously shown to have clear and consistent effects on soil physical properties and soil processes. Our response variables include fungal-related soil processes (decomposition, soil aggregation) and aspects of soil microbial diversity (fungal communities, assessed by Illumina MiSeq high-throughput sequencing). With our field experiment, we hope to test how microplastic effects differ among soil type and environmental context, as well as land use intensity. All experimental items will be removed from the field, assuring that there is no lasting contamination of Exploratory soils. Given that we will only use one microplastic type in the field, and that microplastic pollution is a multifaceted issue, we will also conduct a small-scale, complementary lab experiment, in which we use just one soil type per Exploratory, but add a range of different microplastic types in addition to microfibers. Overall, this research will yield insights into microplastic abundance and effects in soils, making unique use of the wealth of information available for the Exploratories, while at the same time offering a new response variable of potential interest to other researchers (for example in synthesis projects), but also stakeholders.