Microplastics affect belowground performance of winter wheat and microbial networks in the rhizosphere

Microplastics (MPs) are increasingly recognized as environmental pollutants affecting soil ecosystems and plant development, but their specific impacts on plant-soil-microbiome interactions remain unclear. This study investigated the effects of different MP types, including particulate polypropylene (PP), low-density polyethylene (LDPE), polystyrene (PS), and fibrous polyester (PES), individually on early-stage winter wheat root growth, nutrient concentrations, soil conditions and the rhizosphere microbiome using rhizotrons. Our findings revealed that PP and PES MPs significantly reduced root length. We observed increased soil ammonium concentrations with the addition of all MPs, likely due to reduced nitrifying bacterial activity, while PS MP enhanced soil nitrate concentration, potentially reflecting impaired root absorption. Because polymer size and morphology covaried, the results are interpreted as MP-type-specific. No significant effects of MPs on plant potassium (K) and phosphorus (P) uptake were observed. Despite changes in soil nutrient levels, we found no significant alterations in leaf growth, nutrient uptake, or chlorophyll content, indicating that root systems, though affected by MPs, remained sufficiently functional to support shoot development. Microbial co-occurrence analysis revealed two distinct microbial clusters in the rhizosphere, confirming modular microbial structure. Among all treatments, LDPE exposure induced the most pronounced increase in network complexity, as reflected by higher edge density, clustering coefficient, and natural connectivity compared to the control. Many amplicon sequence variants (ASVs), e.g., members of Vicinamibacteraceae, Pseudolabrys and Nitrospira japonica, showed an increased degree and eigenvector centrality in the LDPE treatment, suggesting enhanced co-occurrence and higher influence within the microbial community structure. In contrast, the PES and PP treatments resulted in lower average node degree and reduced clustering. The PS treatment only had a small effect on the microbial co-occurrence networks. Overall, our data indicate that MP-induced stress can alter microbial network topology, reduce community integration, and drive shifts in ecologically important taxa in the rhizosphere, which are linked to changes in the availability of nutrients for plants. Our findings highlight the complex and variable influence of MPs on soil-plant interactions.