For millions of people in developing countries, rice is a staple food. However, as human activities like mining and fossil fuel use increase, arsenic (As) contamination in soil has become a significant and growing threat to crop productivity and human health. Rice is particularly susceptible to arsenic uptake, which can lead to diseases like skin cancer and neurological disorders in people. To address this pressing issue, a study by Mehmood Ali Noor and colleagues, published in the journal Plants, investigated a novel, eco-friendly solution: a combined application of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More (BC) and melatonin (MT).

Biochar is well-known for its ability to immobilize toxic metals and metalloids in soil due to its porous structure and large surface area. Melatonin, a signaling molecule, has also shown promise in mitigating metal toxicity by improving plant growth and reducing oxidative stress. While both substances have been studied individually, this research explored, for the first time, the potential of their synergistic combination to alleviate arsenic toxicity in rice.

Arsenic contamination severely impacts rice plants. The study found that arsenic significantly reduced rice growth and yield by increasing harmful oxidative stress markers like hydrogen peroxide (H2​O2​) and malondialdehyde (MDA), while inhibiting chlorophyll synthesis. In an environment polluted with 100 mg kg⁻¹ of arsenic, the rice plants experienced a 35.17% decrease in grain yield.

The combined application of biochar and melatonin, however, produced remarkable results, exceeding the benefits of either substance alone. The integrated treatment substantially enhanced rice growth and productivity. It boosted chlorophyll synthesis by up to 92.42%, increased leaf water contents by 40%, and most importantly, led to a 31.43% increase in grain yield compared to the arsenic-stressed group. The combination also improved root growth, which is critical for better water and nutrient uptake.

The study’s findings point to several key mechanisms behind this success. The combined treatment significantly increased the activity of antioxidant enzymes (such as ascorbate peroxidase, catalase, peroxidase, and superoxide dismutase) by more than 55%. This enhanced antioxidant defense system protected the rice plants from arsenic-induced oxidative stress. At the genetic level, the combination increased the expression of genes involved in antioxidant and melatonin synthesis, while dramatically decreasing the expression of the gene responsible for arsenic uptake, OsABCC1, by 84.15%. This suppression of the arsenic uptake gene explains why the treatment was so effective at reducing arsenic accumulation in both the roots and shoots of the rice seedlings.

On the soil front, the biochar and melatonin combination significantly reduced arsenic availability in the soil by 74.19% compared to the arsenic-only control. It achieved this by enhancing soil nutrient availability (N, P, and K) and increasing soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More, which helped convert arsenic into more stable forms that are less accessible to plants. The research also found that the treatment increased the presence of organic matter-bound, iron-bound, and manganese-bound forms of arsenic, further immobilizing it in the soil and preventing it from being taken up by the rice plants.

In conclusion, this research demonstrates that the synergistic use of biochar and melatonin is a highly effective and eco-friendly strategy for mitigating arsenic toxicity in rice. By enhancing the plant’s natural defenses, regulating gene expression to reduce arsenic uptake, and immobilizing arsenic in the soil, the combined treatment offers a robust solution for increasing rice productivity and ensuring a safer food supply. While the results are promising, the authors suggest that long-term investigations are needed to validate this practice across different soil and climatic conditions.

Source: Noor, M.A.; Hassan, M.U.; Khan, T.A.; Zhou, B.; Huang, G. Biochar and Melatonin Partnership Mitigates Arsenic Toxicity in Rice by Modulating Antioxidant Defense, Phytochelatin Synthesis, and Down-Regulating the Transporters Involved in Arsenic Uptake. Plants 2025, 14, 2453.