Mechanistic insights into carbon nanomaterials as potential plant biostimulants: enhancing photosynthesis and stress tolerance for climate-resilient agriculture

Abstract

Climate change jeopardizes global food security through increasing temperatures, unpredictable precipitation patterns, and pronounced abiotic stressors including heat, salt, drought, and O₃ that reduce photosynthetic efficiency and crop yield. It likely to cause undernourishment for 1.7 billion people by 2050, exacerbated by population expansion and land degradation. To cope with such challenges, carbon nanomaterials (CNMs) such carbon dots, graphene oxide, and carbon nanotubes are nanostructured materials that show biostimulant-like effects that may improve crop photosynthetic stress tolerance. This review focuses on structure, property, and function of these CNMs in plant systems by elucidating their absorption mechanisms, systemic distribution, and subcellular localization within plant tissues. Mechanistically, CNMs improve photosynthetic efficiency under non-stress conditions by light capture, electron transport, and CO₂ assimilation rates. Under abiotic stress conditions, CNMs exert protective effects on the photosynthetic apparatus by reducing ROS accumulation, stabilizing thylakoid membranes and pigments, modulating stomatal conductance, and enhancing antioxidant enzyme. Their stress-specific ameliorative functions include improving leaf water retention and hydraulic conductivity under drought, ionic homeostasis and Na⁺/K⁺ balance under salinity, protein and membrane integrity under heat stress, and scavenging oxidative radicals under elevated O₃ exposure. Seed priming with CNMs promoted seed germination, improving both seedling vigor and early-stage stress resilience via transcriptomic reprogramming of genes involved in photosynthesis, hormonal signalling, and stress responses. Overall, CNMs support Sustainable Development Goals notably SDG 2 (Zero Hunger), 12 (Responsible Consumption and Production), 13 (Climate Action) and 15 (Life on Land) and hold promise for advancing sustainable agriculture practices. Existing research gaps in CNMs must addressed, including dose-specific variability within plants and the lack of long-term environmental impacts and possible effects on soil microbial communities, as well as limitations in cost-effective and green synthesis methods. Moreover, the legal structures for CNMs in agriculture highlight the importance of multidisciplinary cooperation among nanotechnology experts, toxicology researchers, and policymakers to guarantee the safe utilization of CNMs in sustainable food production systems.