Beyond the audible: the effects of broadband noise pollution on the development of an herbaceous and a woody plant

Although plants and microorganisms can respond to sound (mainly single frequency bands), the effects of anthropogenic noise-particularly broadband traffic noise-remain largely unexplored, especially when plants and soil microbial communities are considered as an integrated system. This study investigates the effects of broadband, traffic-like noise on an herbaceous plant (Trifolium pratense) and a woody species (Ulmus minor), and on its associated soil bacterial communities to improve understanding of noise-related disturbance in urban and roadside ecosystems. A manipulative experiment was therefore conducted in controlled conditions (phytotron chamber), exposing seeds and plants of the two species to broadband noise emissions following a fully orthogonal experimental design, including a control and a treatment (n = 600 seeds). The main morpho-functional traits were then estimated for both species through time. Lastly, the quali-quantitative structure of soil bacterial communities was also assessed. The results showed that broadband noise induced species- and functional type-dependent responses: negative effects were observed in the woody species, whereas the herbaceous species showed neutral to positive responses. No significant effects on soil bacterial communities were detected. Greater sensitivity of woody species may reflect slower growth rates, longer lifespans, and greater structural and physiological complexity, which can limit rapid compensatory responses, particularly during early developmental stages. These findings identify urban broadband noise as a context-dependent stressor with potential implications for roadside vegetation management, urban plant community resilience, and ecosystem functioning in anthropogenic landscapes.