Examining the physiological and molecular impact of biochar on polyol synthesis and drought resistance in tomato plants

Biochar is widely reported to buffer drought by improving soil water-holding capacity and nutrient availability, but whether it also modulates polyol metabolism linked to osmotic adjustment in tomato remains underexplored. Here we integrate physiological (polyol pools, SDH enzyme) and molecular (SDH transcripts) readouts with explicit soil and material characterisation to test how a wood-derived biochar alters the sorbitol/ribitol-SDH axis during water limitation. Tomatoes grown in biochar-amended soil (WB, 20 g kg^-1) versus unamended soil (OB) were exposed to 100%, 75% and 45% soil water content (SWC). Under drought, OB plants accumulated more ribitol and sorbitol, with concomitant increases in SDH activity and SDH mRNA, whereas WB plants showed significantly attenuated polyol accumulation and SDH upregulation. At 75% and 45% SWC, SDH transcripts in OB were ~ 2 × and 4 × the 100% baseline, respectively, versus ~ 1 × and ~ 2 × in WB (two-way ANOVA, irrigation × biochar interaction p < 0.01). Novelty: The data indicate that biochar attenuates the polyol-associated stress response (lower osmolyte demand and SDH induction) while maintaining growth, consistent with improved plant water status. These findings suggest that biochar may contribute to reducing osmotic stress responses, complementing its agronomic benefits in arid systems and supporting sustainable tomato production.