The role of nano-biochar reduces the impact of phenanthrene on wheat photosynthesis†

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants that pose significant risks to the environment and human health. Phenanthrene (PHE), a model PAH, has been shown to cause toxic effects on plants, particularly on their photosynthetic performance. This study investigated the potential of nano-biochar (nBC) derived from rice straw to alleviate the phytotoxicity of PHE in wheat seedlings. We hypothesized that the high adsorption capacity and unique properties of nBC, such as its high surface area, porous structure, and abundant functional groups, could reduce the bioavailability and toxicity of PHE, thereby mitigating its adverse effects on wheat growth and photosynthesis. Wheat seedlings were exposed to different treatments, control, 1.0 mg L⁻¹ nBC, 1.0 mg L⁻¹ PHE, 1.0 mg L⁻¹ PHE + 0.5 mg L⁻¹ nBC, and 1.0 mg L⁻¹ PHE + 1.0 mg L⁻¹ nBC. The results showed that nBC alleviated PHE-induced chlorosis and improved plant growth. Compared to the PHE-single treatment, the application of 1.0 mg L⁻¹ nBC increased chlorophyll content by 14.54% and enhanced photosynthetic efficiency, as evidenced by increases in Fv/Fm (2.48%), q_P (9.06%), and Φ_PSII (3.81%). Furthermore, nBC reduced the accumulation of PHE in wheat tissues, with the PHE concentration in the PHE-single treatment being 1.77 and 1.61 times higher than that in the 1.0 mg L⁻¹ nBC treatment for shoots and roots, respectively. The non-photochemical quenching (NPQ) values decreased by 13.64% in the presence of 1.0 mg L⁻¹ nBC, indicating reduced heat dissipation and improved photosynthetic performance. The alleviation of PHE toxicity by nBC can be attributed to its high adsorption capacity, which limits the uptake of PHE by plants. Additionally, the photoelectric effect of nBC may directly promote photosynthesis by enhancing electron transport and providing reducing power for ATP and NADPH synthesis. The use of nBC for the remediation of PAH-contaminated soils offers several advantages, including sustainability, eco-friendliness, and additional benefits such as carbon sequestration and soil quality improvement. These findings highlight the potential of nBC as an effective amendment for the remediation of PAH-contaminated soils and the protection of crops under PAH stress.