Effectiveness of sulfur-modified wheat straw biochar in alleviating vanadium stress in rice: impacts on growth, photosynthesis, and redox regulation

Abstract Vanadium (V) is recognized as an environmental contaminant that adversely affects plant growth and development. The main objective of this study was to investigate the effects of sulfur-modified biochar (SBC) compared to standard biochar (BC) on rice under V suppression (35 mg L −1 ). Our findings revealed that V stress significantly suppressed rice seedling growth, evidenced by reductions in shoot fresh weight, chlorophyll pigment content, photosynthetic assimilation, and root attributes, with higher V accumulation observed in both shoots and roots of V-stressed plants compared to BC- and SBC-treated plants. SBC application improved rice growth more effectively than BC, exhibiting increases of 61.41% in fresh weight, 63.04% in root length, 66.66% in chlorophyll a, 52.20% in chlorophyll b, and 52.95% in carotenoids, alongside enhanced gas exchange attributes. Notably, SBC reduced V accumulation by 58.33% in shoots and 43.79% in roots compared to V-stressed plants. SBC also induced V stress tolerance in rice by elevating antioxidant enzyme activities in roots and shoots, including superoxide dismutase (SOD, 85.25/89.41%), catalase (CAT, 119.04/100.01%), glutathione peroxidase (GPX, 82.20/79.82%), glutathione S-transferase (GST, 123.74/114.67%), ascorbate peroxidase (APX, 86.56/63.74%), glutathione reductase (GR, 204.87/60.36%), dehydroascorbate reductase (DHAR, 53.60/62.06%), and monodehydroascorbate reductase (MDHAR, 87.09/88.88%), while simultaneously reducing hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) levels. Furthermore, SBC increased the activities of glyoxalase enzymes (Gly I by 96.15/77.14% and Gly II by 115.78/104.25%), mitigating methylglyoxal (MG) induced toxicity, and enhanced the expression of metal-tolerant ( OsFSD1 ) genes and antioxidant-glyoxalase systems. Overall, SBC application was found to be more effective than raw BC in alleviating V-induced toxic effects and improving rice plant growth. Nonetheless, further studies must be performed to determine exactly driving mechanism involved in the promotion of growth. Graphical Abstract