Systemic regulation of plant root traits and root-mycorrhizal symbiosis by elevated CO₂

Climate change, a major threat to global food security, has been accelerated by increasing atmospheric CO₂ levels over the last two centuries. Numerous studies indicate that high atmospheric CO₂ (eCO₂) enhances carbon (C) sequestration in plant biomass, potentially aiding in its mitigation. Plant root characteristics are critical regulators of underground C inputs, soil nutrient acquisition, and water uptake. Roots directly interface with soil, while shoots perceive atmospheric CO₂ via β-carbonic anhydrase, triggering systemic signals, such as hormone pathways, that influence root functions, including strigolactone secretion and mycorrhizal colonization. Recent research has begun to elucidate how eCO₂ influences root morphology, root system expansion, and overall root functionality, including increased root:shoot ratios, respiration rates, rhizodeposition, and fungal colonization. This review aims to synthesize the current understanding of eCO₂ effects on plant roots, with a particular focus on arbuscular mycorrhizal (AM) symbiosis. We highlight novel findings regarding the interactions between eCO₂ and plant hormones, which play a crucial role in the systemic regulation of AM symbiosis. Finally, we outline potential future research directions that could enhance crop resilience to climate change, emphasizing the importance of integrating root biology and mycorrhizal interactions in sustainable agricultural practices.