Combination of biochar and silicon influenced the leaf structure, phytochemical properties and yield of triticale under lead-contaminated soil

Heavy metal (HM) contamination of agricultural soils threatens food security by impairing plant growth and productivity. Although biochar and silicon (Si) are individually known to alleviate HM stress, their synergistic effects on the anatomical and biochemical traits of triticale remain poorly understood. This study investigated the application of Si (0, 200, and 400 mg kg −1 soil) with four biochar types including no biochar application (C), sheep manure biochar (SMB), rice husk biochar (RHB), and municipal waste biochar (MWB) on triticale (X Triticosecale Wittmack) leaves under lead (Pb) toxicity (500 mg kg −1 soil) using a factorial pot experiment based on a completely randomized design. Results revealed that treatment efficacy was strongly dependent on both Si dosage and biochar type. The most pronounced improvements were achieved with SMB applied at 200 mg Si kg −1 (Si200), which increased leaf weight and leaf area by 108.3% and 29.7%, respectively, compared to control. These enhancements were associated with significant developmental changes in vascular tissues, including increased areas of midrib, metaxylem and protoxylem, which facilitated improved water and nutrient transport under Pb-stressed conditions. However, increasing the Si supply to 400 mg kg −1 reversed these positive effects and caused a notable reduction in stomatal area, indicating the existence of an optimal dosage threshold. SMB at Si 200 significantly improved membrane stability and enhanced total chlorophyll content by 101.3%, while also elevating carotenoid levels as part of protective response. Additionally, increasing catalase (CAT) and peroxidase (POX) activities in SMB at Si 200 , reflecting superior oxidative stress mitigation. At Si 400 , RHB proved less effective, reducing stomatal area by 25.6% compared to SMB, highlighting the superior performance of SMB under higher Si levels. The structural and biochemical improvements with SMB at Si 200 increasing plant height (19.8%), total dry matter (69.5%), grains per spike (65.8%), and grain yield (68.0%) relative to control. These results demonstrate that application of 200 mg Si kg −1 soil with SMB represents a synergistic and effective strategy for reclaiming Pb-contaminated soils. Nevertheless, excessive Si supplementation produces antagonistic effects, emphasizing the critical need for precise dosage optimization in field applications.