Effect of microplastics on rhizosphere and arbuscular mycorrhizal fungi of Zea mays

Microplastics (MPs) in agricultural soils present an emerging environmental challenge, yet their effects on soil microbiota remain under-explored. This study investigates the impacts of two types of pre-treated polyethylene (PE1 and PE2) MPs on the rhizosphere and arbuscular mycorrhizal fungi (AMF) of Zea mays. Zea mays were treated with MPs (0.1% and 0.5% w/w, n=9) and grown under glasshouse conditions for seven weeks. Five different rhizosphere fungi were isolated from MPs untreated maize rhizosphere soil (control) and tested on their growth impact in vitro on Potato Dextrose Agar enriched with variable concentrations of MPs (0.1%, 0.5%, and 2% w/v; n=3). AMF root colonization, spore abundance, and morphotype richness were significantly reduced in a concentration-dependent manner, with PE1 causing highest impact. At 0.5% w/w, AMF colonization rates declined to 13.8% and 17.5% for PE1 and PE2, respectively, compared to their corresponding controls of 62.1% and 50.9%. This represents a 77.8% reduction for PE1 and a 65.6% reduction for PE2, indicating a substantial inhibitory effect of MPs on AMF root colonization. In petri plate assay, RF1 exhibited a notable growth rate of 0.807 ± 0.006 cm/day under control conditions, which declined by approximately 70% at 2.0% w/v in the presence of PE1. Similar trends were observed in other isolates, where increased concentrations resulted in significant growth inhibition while RF5 exhibiting a significant 120% reduction at 2% w/v PE1 (growth rate: 0.208 ± 0.02 cm/day), suggesting that MPs may exert toxic effects on fungal metabolism and growth. This study highlights the detrimental effects of MPs on rhizosphere fungi, including AMF, suggesting that MPs pose a significant threat to soil microbiota and plant-microbe interactions, with potential implications for agricultural sustainability.