Silicon-mediated drought resilience mechanisms in crops: from physiology to molecular insights.

Drought stress increasingly constrains crop growth, yield, and quality through reduced photosynthesis, impaired nutrient uptake, and oxidative damage, with recent occurrences causing substantial yield losses across major production regions. Silicon (Si), although not an essential nutrient, is a prevalent, non-toxic, "quasi-essential" element that can enhance crop performance under water limitation; however, Si-induced drought-mitigation mechanisms are frequently reported in isolation, based on individual studies. This review aims to provide a holistic understanding of Si's role in enhancing plant resilience to water stress by comprehensively compiling and integrating physiological to molecular mechanisms underpinning Si-mediated drought resilience, while contextualising soil Si availability, plant uptake and accumulation diversity, and agronomic delivery options. Across crops, Si fertilisation consistently improves water relations by promoting root growth, hydraulic conductance, and aquaporin regulation, enabling osmotic adjustment and modulating stomatal behaviour through hormone-reactive oxygen species interactions. Evidence is synthesised from controlled and field studies, alongside temporal trend analyses showing a shift from uptake/transport research (pre-2010) to physiological characterisation (2010-2015), and to integrative multi-omics (2020-present), including transcriptomics and metabolomics. Key research gaps include limited field validation, inconsistent experimental designs and drought imposition protocols, incomplete multi-omics-to-trait integration, and underexplored Si-microbiome interactions. Optimising the Si source, dosage, timing, and application method across different species and environments presents a practical approach to developing climate-resilient, low-input cropping systems in the face of increasing drought risk.