Plant Soil Environ., 2025, 71(8):534-552 | DOI: 10.17221/239/2025-PSE

Wheat (C3) and maize (C4) adaptive responses to soil thallium toxicity under elevated CO₂ conditionsOriginal Paper

Wael A. Obaid¹, Samy Selim², Seham M. Hamed³, Emad A. Alsherif⁴, Shereen Magdy Korany⁵, Hana Sonbol⁵, Danyah A. Aldailami⁶, Soad K. Al Jaouni⁷

¹ Biology Department, College of Science, Taibah University, Al-Madinah Al-Munawwarah, Saudi Arabia

² Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Jouf University, Sakaka, Saudi Arabia

³ Department of Biology, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh, Saudi Arabia

⁴ Department of Botany and Microbiology, Faculty of Science, Beni-Suef University, Beni-Suef, Egypt

⁵ Department of Biology, College of Science, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia

⁶ Public Health Department, College of Health Sciences, Saudi Electronic University, Riyadh, Saudi Arabia

⁷ Department of Haematology/Oncology, Chair of Prophetic Medicine Application, Faculty of Medicine, King Abdulaziz University, Jeddah, Saudi Arabia

This study investigated how wheat (C3) and maize (C4) respond to soil thallium (Tl) contamination and elevated CO₂ (eCO₂), aiming to understand strategies for mitigating oxidative stress. Under eCO₂, both crops showed higher biomass production. However, high Tl concentration (120 mg/kg) significantly decreased fresh and dry weights by 31–59%, which translated directly to compromised yield. This growth decline is linked to impaired photosynthesis, evidenced by a 54–57% drop in net photosynthetic rate under elevated Tl. Such photosynthetic inhibition intensifies oxidative stress, marked by increased membrane damage and hydrogen peroxide (H2O2). Furthermore, photorespiration contributed to oxidative stress by generating H₂O₂, with increased activities of glycolate oxidase and hydroxypyruvate reductase rising by 122% and 201%, in wheat and by 179% and 39% in maize, respectively, in response to 120 mg/kg TI under eCO₂ conditions. Simultaneously, to mitigate oxidative damage, antioxidant defences were significantly enhanced, resulting in increased activity of the ascorbate (ASC)/glutathione (GSH) cycle, along with elevated levels of metallothionein and phytochelatin for Tl sequestration, as well as augmented glutathione S-transferase activity. Overall, findings reveal complex interactions between CO₂ and Tl, highlighting species-specific adaptive responses of C3 and C4 plants. C3 plants use photorespiration to combat oxidative stress, while C3 and C4 plants have strong antioxidant systems to reduce the effects of oxidative stress, promoting crop resilience and growth despite Tl toxicity.

Keywords: climate changes; functional group; heavy metal; redox status; detoxification

Received: May 31, 2025; Revised: July 12, 2025; Accepted: July 23, 2025; Prepublished online: August 12, 2025; Published: August 28, 2025  Show citation