Table 1_Integrative biochar and melatonin application mitigates lead toxicity in rice by modulating antioxidant activities and iron plaque formation and downregulating the expression of metal uptake genes.docx

Lead (Pb) is a common toxic metal that causes severe health and environmental problems. However, the defensive role and underlying mechanism of combined biochar (BC) and melatonin (MT) against Pb stress are still unclear. Therefore, to fill this gap, this study investigated the impacts of BC and MT on rice growing in Pb-polluted soil. This study included different treatments: control, Pb stress (300 mg kg−1), Pb stress (300 mg kg−1) + BC (2%), Pb stress (300 mg kg−1) + MT (30 µM), and Pb stress (300 mg kg−1) + BC (2%) + MT (30 µM). Pb reduced rice growth and yield by hindering photosynthetic pigments, relative water contents (RWCs), osmolyte synthesis, nutrient uptake, increase in oxidative markers, and Pb accumulation. Biochar and MT increased rice productivity by increasing chlorophyll synthesis, osmolytes, and nutrient uptake and decreasing Pb accumulation. The co-application of BC and MT decreased Pb accumulation in the roots (30.40%) and shoots (72.79%), the translocation factor (30.01%), the biological accumulation coefficient (20.17%), and the soil Pb concentration (59.02%). The co-application of BC and MT enhanced proline (39.65%), soluble protein (47.09%), ascorbate peroxidase (APX; 26.47%), catalase (CAT; 65.51%), peroxidase (POD; 89.56%), and superoxide dismutase (SOD; 65.53%) activities, which ensured better productivity. Additionally, the BC+MT application increased the expression of antioxidant defense genes (OsAPX, OsCAT, OsPOX, and OsSOD) and decreased the expression of metal transporter genes (OsHMA9 and OsNRAMP5), which protected the rice plants from damage caused by Pb toxicity. These results suggested that BC+MT could be a promising strategy to mitigate Pb toxicity and maintain sustainable and safer food production.

铅（Lead, Pb）是一种常见的有毒重金属，可造成严重的健康危害与环境问题。然而，生物炭（Biochar, BC）与褪黑素（Melatonin, MT）联合施用缓解铅胁迫的防御作用及其潜在机制仍未明确。为此，本研究旨在填补这一研究空白，探究生物炭与褪黑素对铅污染土壤中水稻生长的影响。本研究设置了5组不同处理：空白对照组、铅胁迫组（300 mg·kg⁻¹）、铅胁迫组（300 mg·kg⁻¹）+生物炭（2%）、铅胁迫组（300 mg·kg⁻¹）+褪黑素（30 μM），以及铅胁迫组（300 mg·kg⁻¹）+生物炭（2%）+褪黑素（30 μM）联合处理组。铅胁迫通过抑制光合色素合成、降低植株相对含水量（Relative Water Contents, RWCs）、阻碍渗透调节物质合成与养分吸收，同时提升氧化应激标志物水平与植株铅积累量，进而抑制水稻生长与产量形成。生物炭与褪黑素可通过促进叶绿素合成、提升渗透调节物质含量与养分吸收效率，同时降低植株铅积累量，从而提高水稻产量。生物炭与褪黑素联合施用可分别降低水稻根系铅积累量30.40%、地上部铅积累量72.79%，同时使转运系数（Translocation Factor, TF）下降30.01%、生物富集系数（Biological Accumulation Coefficient, BCF）下降20.17%，并降低土壤铅浓度59.02%。联合施用生物炭与褪黑素还可提升水稻体内脯氨酸（增幅39.65%）、可溶性蛋白（增幅47.09%）、抗坏血酸过氧化物酶（Ascorbate Peroxidase, APX，增幅26.47%）、过氧化氢酶（Catalase, CAT，增幅65.51%）、过氧化物酶（Peroxidase, POD，增幅89.56%）以及超氧化物歧化酶（Superoxide Dismutase, SOD，增幅65.53%）的活性，保障水稻良好的生长与产量表现。此外，生物炭与褪黑素联合施用可上调抗氧化防御基因（OsAPX、OsCAT、OsPOX与OsSOD）的表达水平，同时下调金属转运蛋白基因（OsHMA9与OsNRAMP5）的表达，从而保护水稻植株免受铅毒性损伤。上述研究结果表明，生物炭与褪黑素联合施用是缓解铅毒性、实现粮食可持续安全生产的极具潜力的可行策略。