Plant Soil Environ., 2025, 71(9):666-679 | DOI: 10.17221/328/2025-PSE

Species-specific responses of wheat and maize to thallium stress under elevated CO₂: effects on yield, photosynthesis, and metabolismOriginal Paper

Samy Selim Abdelsalam¹, Soad K. Al Jaouni², Seham M. Hamed³, Emad A. Alsherif⁴, Afrah E. Mohammed^5,6, Modhi O. Alotaibi⁵, Danyah A. Aldailami⁷, Wael A. Obaid⁸

¹ Department of Clinical Laboratory Sciences, College of Applied Medical Sciences, Jouf University, Sakaka, Saudi Arabia

² Department of Haematology/Oncology, Chair of Prophetic Medicine Application, Faculty of Medicine, King Abdulaziz University and Hospital, Jeddah, 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 Microbiology and Immunology Unit, Natural and Health Sciences Research Centre, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia

⁷ Public Health Department, College of Health Sciences, Saudi Electronic University, Riyadh, Saudi Arabia

⁸ Biology Department, College of Science, Taibah University, Al-Madinah Al-Munawwarah, Saudi Arabia

Heavy metal stress inhibits plant growth, but this impact is less studied and pronounced under climate change conditions. The present study investigates the physiological, biochemical, and agronomic responses of wheat (C3) and maize (C4) exposed to varying thallium (Tl) stress (60 and 120 mg/kg) under ambient (aCO₂) and elevated (eCO₂, 710 µmol/mol) CO₂ levels. High Tl exposure markedly reduced grain yield by 58% in wheat and 68% in maize at 120 mg/kg under aCO₂. However, eCO₂ partially offset the negative effects, increasing yield by ~20% in wheat and 36% in maize at 60 mg/kg Tl. eCO₂ enhanced photosynthetic activity under eCO₂, which increased the accumulation of soluble sugars under TI stress. These provide carbon skeletons for the synthesis of primary metabolites such as amino acids, organic acids and fatty acids. Although total fatty acid content declined under stress, the metabolic crosstalk initiated by improved photosynthesis and sugar availability enables plants to maintain key fatty acids (such as palmitic, linolenic, and oleic acids) essential for membrane stability and function. Amino acids, especially proline and cysteine, accumulated significantly under Tl stress. These primary metabolites, in turn, feed into secondary metabolic pathways, promoting the formation of phenolic acids and flavonoids that enhance antioxidant defence and stress tolerance. This metabolic cascade explains eCO₂’s capacity to alleviate TI stress and improve crop performance, and underscores the value of leveraging eCO₂ environments to support agricultural productivity and food security under challenging conditions.

Keywords: C3 and C4 plants; environmental toxicity; physiological responses; Triticum aestivum L.; Zea mays L.

Received: July 26, 2025; Revised: September 17, 2025; Accepted: September 18, 2025; Prepublished online: September 25, 2025; Published: September 26, 2025  Show citation