Combination of biochar and silicon influenced the structural and phytochemical characteristics of triticale leaf under soil lead toxicity

Heavy metal (HM) contamination of agricultural soils poses a significant environmental challenge, threatening food security due to decreased plant growth and agricultural production. This study aimed to investigate the synergistic effects of silicon (Si) combined with biochar on the structural and phytochemical properties of triticale leaf under lead (Pb)-contaminated soil. A factorial pot experiment was carried out using a completely randomized design (CRD) to examine the effects of Si (0, 200, and 400 mg Si kg⁻¹ soil) in combination with sheep manure biochar (SMB), rice husk biochar (RHB), and municipal waste biochar (MWB) under Pb toxicity (500 mg Pb kg⁻¹ soil). The application of SMB at 200 mg Si kg⁻¹ (Si200) enhanced leaf weight and area by 108.3% and 29.7%, respectively, compared to the control (without Si and biochar). Increasing the Si application level from 0 to 200 mg kg⁻¹ soil significantly increased the areas of the midrib, metaxylem, and protoxylem; however, a further increase to 400 mg Si kg⁻¹ (Si400) led to a gradual decline in these traits under Pb-contaminated conditions. At Si400, RHB was less effective in mitigating Pb toxicity, resulting in a 25.6% reduction in stomatal area compared to SMB. Additionally, at Si0 and Si200, SMB demonstrated greater efficacy in enhancing the membrane stability index compared to Si400. The application of SMB at Si200 and RHB at Si0 improved total chlorophyll content by 101.3% and 94.5%, respectively. A notable increase in carotenoid content was observed with biochar application under Pb toxicity. The highest values of catalase (CAT) and peroxidase (POX) activity were recorded in SMB at Si200, with increases of 56.6% and 32.9%, respectively, compared to the control. Overall, the application of Si200 with SMB significantly enhanced plant height (19.8%), total dry matter (69.5%), number of grains spike-1 (65.8%), and grain yield (68.0%) compared to the control. These enhancements were related to increases in leaf area, leaf weight, midrib area, chlorophyll content, enzyme activity, and relative water content.