Harnessing mediterranean plant-microbiota systems for anti-pollution noise barriers

Mitigation of urban air pollution caused by vehicle and industrial activities is urgently needed to reduce harmful impacts on human health and ecosystems. In this context, plants are effective agents of pollution mitigation, acting as bioaccumulators of gaseous hydrocarbons and particulate matter (PM10, PM2.5) through stomatal uptake and leaf deposition. The phyllosphere microbiota (i.e., microbial communities on leaf surfaces) enhance air pollutants removal through adsorption and biodegradation, utilizing atmospheric contaminants as nutrient sources [1]. Beyond phyllosphere, every plant compartment hosts a dynamic microbiota that modulates plant physiology and fitness. Among the beneficial relationships, arbuscular mycorrhizal (AM) symbiosis, legume-nitrogen fixing symbiosis and plant growth-promoting (PGP) bacteria interactions are the most widespread. Based on these principles, the project ECOROADS (funded under the PON Research and Innovation program and led by ANAS S.p.A.), aims to reduce noise and air pollution generated by vehicles through a multifunctional and bioengineered anti-noise road barrier, to be built in Sicily as a prototype. To this aim, local plant species inoculated with their microbial symbionts will be integrated into the core of the noise barrier and placed along the adjacent slope in a high-traffic road, near sensitive sites. The barrier will host a selection of Mediterranean plants characterized by specific functional traits: shrubs and small trees (e.g., Myrtus communis), nitrogen-fixing legume shrubs (e.g., Anagyris foetida, Spartium junceum), and aromatic plants (e.g., Salvia rosmarinus, Thymus capitatus). The adjacent slope will be also planted and reinforced with structural trees (e.g., Fraxinus ornus and Quercus ilex). The phyllosphere of the plants will be harnessed through the application of selected drought tolerant hydrocarbon-degrading actinobacteria [2]. To enhance plant survival and resistance against extreme environmental conditions of the barrier, each plant rhizosphere will be boosted through the inoculation of PGP microorganisms sourced from the MIRRI-UNIPA collection or provided by specialized collections. Moreover, the rhizosphere of Mediterranean legumes will be inoculated with indigenous, nitrogen-fixing rhizobia [3] and AM fungi that successfully promoted plant growth in anthropogenic soils [4]. Aromatic shrubs will be inoculated with AM fungi and PGP actinobacteria, whose efficacy was previously demonstrated on Mediterranean crops and aromatics [5]. Together, these specific microbial inoculants will enable the integrated system to function as an active biological filter, transforming traditional road barriers into a sustainable solution for air purification.