From root exudates to lime amendments: mechanistic insights and effective remediation of aluminum toxicity in acidic soils

: Soil acidification affects approximately 40–50% of global arable land, and Al toxicity is the primary constraint on crop productivity in soils with pH below 5.5. Below this threshold, Al is released at phytotoxic concentrations that inhibit root elongation, impair nutrient uptake, and induce oxidative stress in sensitive crops. Where the topsoil pH can be corrected to above 5.5, routine liming remains the most effective and economically rational strategy. Previous reviews have addressed acidification mechanisms or plant tolerance physiology in isolation, without evaluating liming performance boundaries or defining when complementary strategies are warranted. This review traces the mechanistic continuum from soil acidification through Al speciation to phytotoxicity, and examines plant tolerance pathways governed by transcription factor-regulated organic acid transporter networks. Liming serves as the performance baseline against which five remediation categories are evaluated: inorganic and nutrient-based amendments, organic matter and biochar, controlled-release alkaline materials, microbial inoculants, and Al-tolerant cultivars. Three research frontiers limiting the translation of mechanistic knowledge to field practice were identified as: (1) in situ characterization of Al speciation dynamics in the rhizosphere; (2) predictive modeling of amendment performance using multi-year field datasets; and (3) the gap between laboratory efficacy of functional materials and validated field outcomes. A soil-diagnosis decision framework is proposed linking amendment selection to soil pH, Al speciation, co-existing stresses, and site-specific constraints. Routine liming is sufficient where topsoil pH can be raised above 5.5; scenario-based interventions are warranted only when subsoil acidity, rapid re-acidification, Al-P co-limitation, or PTE co-contamination represent binding constraints.