Alleviating Effect of Silicon on Aluminum Toxicity in Plants

Aluminum (Al) toxicity is a major constraint on crop growth and productivity in acidic soils, affecting root development, nutrient uptake, and photosynthetic performance. The use of Si is a promising strategy to overcome the adverse effects of Al toxicity on species of agronomic interest. Between 2020 and 2026, 15 studies across nine species consistently demonstrated that silicon mitigated aluminum toxicity, regardless of their classification as silicon accumulators. In plants, Si mitigates Al toxicity through a combination of physical, chemical, and biochemical mechanisms that operate simultaneously. In the rhizosphere, Si interacts directly with Al3+ ions, favoring the formation of hydroxyaluminosilicates (HASs), which reduces the bioavailable fraction of Al. Evidence indicates that solution pH is a critical factor governing HAS formation, with minimal attenuation of Al toxicity observed at pH values below 4.5. Within the plant, Si modulates the antioxidant defense system by enhancing the activity of enzymes such as catalase, peroxidase, and ascorbate peroxidase, thereby reducing oxidative stress typically triggered by Al toxicity. Moreover, Si influences the biosynthesis of lignin and phenolic compounds with Al-chelating capacity, contributing to detoxification at the cellular level. In soybean and rice, Si supply substantially reduced Al deposition in the root apical cell wall, with decreases of approximately 52% and 41.3%, respectively. This reduction was consistently associated with improved root elongation, maintenance of root structural integrity, mitigation of cellular deformation, and preservation of root thickness and vascular organization. Although these mechanisms have been described, a comprehensive synthesis of studies published from 2020 to 2026 has been lacking, particularly regarding the integration of in-plant processes and species-specific responses. This review fills this gap by critically examining recent findings, highlighting the multifaceted role of Si in alleviating Al stress, and discussing implications for agronomic applications in acidic soils. Collectively, the evidence underscores Si as an effective tool to enhance plant tolerance to Al; however, most available evidence is derived from early plant developmental stages and hydroponic or highly controlled systems, which limits the direct extrapolation of these findings to soil and field conditions. Future advances will require studies under soil environments, accounting for species-specific responses, soil properties, management systems, and plant developmental stages.