Impact of Pyrogenic Carbon on Tomato Root Architecture and Metabolites (ABA and Proline)Root Exudates under Drought Stress

Yuan Zhang¹Riffat-un- Nisa²Aansa Rukya Saleem^2*Waqar Un Nisa³Abubakr M Idri⁴Guo Yu¹Habib Ullah^5*

• ¹Guilin University of Technology, Guilin, China
• ²Bahria University, Islamabad, Pakistan
• ³International Islamic University Islamabad, Islamabad, Pakistan
• ⁴King Khalid University, Abha, Saudi Arabia
• ⁵Zhejiang University, Hangzhou, China

Drought stress poses severe threat to global agriculture, significantly reducing crop productivity and compromising food security. Addressing this challenge, biochar derived from agricultural waste has emerged as a promising soil amendment to improve plant resilience and mitigate drought impacts. This study investigates effects of walnut shell biochar (WS biochar) on tomato (Solanum lycopersicum) growth under varying drought conditions (severe at 45% field capacity and moderate at 75% field capacity). Two biochar application rates, 3% and 5% (w/w), were tested for their influence on root architecture, biomass accumulation, and stress-related hormonal responses. Formatted: Italic WS biochar showed a high conversion efficiency of 58.8% and favorable physicochemical properties, including high fixed carbon content (98%) and low volatile matter (2.4%), making it suitable for long-term soil amendment. Scanning electron microscopy revealed a porous macroporous structure with fissured textures enhancing water retention and soil aeration. Elemental analysis indicated a carbon content of 54.7% and oxygen content of 41.2%, consistent with stable lignocellulosic biochar. Biochar amendments significantly improved plant growth metrics under drought stress. The 5% biochar treatment enhanced plant height by 24% compared to controls and increased leaf production, indicating improved plant foliar development. Biomass measurements showed that biochar application mitigated the 92% biomass reduction observed under severe drought, with the 5% treatment maintaining significantly higher fresh and dry weights. Enhanced root architecture, characterized by 30% longer primary roots and 25% higher lateral root density, was evident in biochar-amended plants, supporting improved water uptake and drought tolerance. Physiological analyses revealed reduced proline accumulation and abscisic acid (ABA) levels in biochar-treated plants, indicating lowered oxidative stress and improved water status. The 5% biochar treatment reduced proline by 18% and ABA by 22% under severe drought conditions relative to controls. These hormonal modulations suggest that biochar may contribute to improved drought resilience biochar ameliorates drought stress through enhanced soil water retention and altered root hormonal signaling. The findings underscore biochar's potential as sustainable, climatesmart soil amendment to support crop production in water-limited environments. Further field-scale studies are warranted to validate long-term impacts on soil health and crop yield.