Background and aims <p>Arsenic (As) contamination is a major environmental stressor that limits plant growth and productivity. While silicon (Si) is reported to mitigate stress, its effectiveness and mechanisms of action remain context-dependent. Here, we investigated the root-type specific responses of two maize hybrids (Tweetor and Luciana) to As stress (75 and 150&#xa0;µM) with or without silicon (Si) supplementation, with the focus on phenylpropanoid metabolism, lignification, and growth.</p> Methods <p>Histochemical detection of lignin and total root lignin and phenolics were assessed in different root types (main, seminal adventitious and nodal adventitious roots). Moreover, the activities of key enzymes involved in phenylpropanoid pathways and the expression of related genes were compared.</p> Results <p>Arsenic significantly inhibited root elongation, particularly in main and seminal roots, whereas nodal roots exhibited higher plasticity and responsiveness to Si. Analysis revealed differences in activation of the phenylpropanoid pathway, with tyrosine ammonia-lyase (TAL) exhibiting a stronger stress-induced response than phenylalanine ammonia-lyase (PAL). This suggests a shift toward tyrosine as a precursor to lignin biosynthesis under As stress. Tested hybrids showed contrasting defence strategies: Tweetor accumulated more soluble phenolics, indicating enhanced non-enzymatic antioxidative capacity; however, Luciana had stronger lignification and higher enzymatic antioxidant activities, reflecting structural and enzymatic reinforcement.</p> Conclusion <p>Maize responses to As were significantly dependent on the root category and genotype. Silicon only partially alleviated As stress and did not consistently restore enzyme activities or gene expression despite stimulating growth and phenolic metabolism under non-stress conditions. Findings also highlight the importance of integrating the whole root system heterogeneity into strategies improving crop stress tolerance.</p>