Driving soils to change: Tyre wear particles modulate microbial-mediated soil functions and performance of vegetable crops

Summary

Tyre wear particles (TP) enter soils through various pathways, accumulate over time and can affect plant-soil systems. However, the effects of TP, particularly on the microbiota, are not well understood and the potential risks to soil ecosystems remain uncertain. We added TP at concentrations ranging from 0 % to 3 % (w/w) to a sandy loam soil and conducted an experiment with lettuce and leek. We assessed how TP affect plants, the colonisation of their roots with arbuscular mycorrhizal fungi (AMF), soil enzymatic activities and microbial catabolic profiles. Exposure to 3 % TP reduced root and shoot biomass by 35 % and 23 %, respectively, relative to the control, while lower TP levels showed some stimulating effects. Also, a TP addition of 3 % increased plant copper and zinc concentrations but decreased plant nitrogen. We did not find effects on AMF colonisation, yet, these findings are based on the staining method only and should be studied in more depth using additional methods. Some soil enzymes showed a high sensitivity to even the lowest TP concentrations. Furthermore, in soils containing 3 % TP, we measured a reduction in the microbial biomass carbon (up to −20 %), an increase in the microbial metabolic quotient (up to +62 %), and significant changes in the catabolic capacity of soil microbes. Our data show that TP can affect the microbial basis of the soil food web and specific processes related to soil nutrient and energy flow, with ultimate effects on plants. Although the mechanisms cannot be fully displayed with the data at hand, our study stresses the urgent need to implement measures that reduce TP pollution to safeguard soil quality and allow the production of healthy food crops.