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Co-application of biochar and melatonin enhances rice resilience to combined lead and microplastics stress via modulating antioxidant defense, hormonal regulation, gene expression, and soil quality
Summary
Lead pollution and microplastics in soil team up to stunt rice growth and reduce harvests — a real concern since rice is a staple food for billions. This study found that adding charcoal-like "biochar" plus melatonin (a natural compound) to contaminated soil helped rice plants defend themselves, absorb less lead, and produce nearly as much grain as healthy plants, suggesting a practical way to grow safer food in polluted farmland.
Abstract Background Microplastics (MPs) pollution is becoming a serious challenge and poses ecological risks. MPs are known to interact with heavy metals, such as lead (Pb), adversely impacting plant growth. Both biochar (BC) and melatonin (MT) have been extensively utilized in soil remediation efforts. However, the combined effect of BC and MT in alleviating the combined toxicity of Pb and MPs has not been investigated. Methodology The study included various treatments: T1: control, T2: Pb (250 mg kg− 1) + MPs (1%), T3: Pb (250 mg kg− 1) + MPs (1%) + BC (2%), T4: Pb (250 mg kg− 1) + MPs (1%) + MT (100 µM) and T5: Pb (250 mg kg− 1) + MPs (1%) + BC (2%) + MT (100 µM). Results Lead + MPs reduced the rice biomass yield (BY: 25.26%) and grain yield (GY: 41.51%) by increasing the hydrogen peroxide (H2O2), malondialdehyde (MDA), Pb accumulation, and decreasing the indole acetic synthesis (IAA), gibberellic acid synthesis (GA), transpiration rate (Tr), photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 (Ci), soil nitrogen, phosphorous and potassium availability. The combination of BC + MT enhanced rice BY (18.20%) and GY (39.59%) by increasing IAA (36.75%), GA (41.90%), Pn (32.35%), Tr (37.15%), gs (44.44%), and Ci (20.69%) and decreasing the production of MDA and H2O2 by increasing the antioxidants activity (41.17–52.55%). Furthermore, the combined application of BC and MT resulted in the upregulation of antioxidant genes (OsAPx6, OsCAT, OsPOD, and OsSOD), melatonin synthesis gene (OsASMT1), and proline biosynthesis gene (OsP5CS), while concurrently downregulating genes associated with lead uptake (OsHMA9 and OsNRAMP5). The BC + MT treatment also improved soil total nitrogen (TN) by 28.19%, available phosphorus (AP) by 26.73%, and available potassium (AK) by 18.81%, alongside an increase in soil pH. Additionally, it reduced soil lead availability by 37.18%, collectively contributing to enhanced rice biomass and grain yield. Conclusion Thus, BC + MT can alleviate adversities of Pb + MPs by improving soil fertility, plant functioning, hormonal balance, and gene expression. These findings offer insights to develop measures to enhance the crop in multi-polluted soils.