Root system growth and development responses to elevated CO₂: underlying signalling mechanisms and role in improving plant CO₂ capture and soil C storage

Carbon storage in soils is one of the most promising strategies for mitigating greenhouse gas emissions and the associated climate change. In this context, how plant root systems respond to the elevation of the atmospheric CO₂ concentration is of crucial importance because these organs are the main source of C input into the soils. It is expected that root growth will be stimulated by elevated CO₂ as a consequence of enhanced photosynthesis, and that this will favour belowground C sequestration. In addition, larger root systems with optimized architecture are also expected to improve water and nutrient acquisition by plants, and to indirectly stimulate photosynthetic CO₂ capture. This review critically examines the evidence supporting these expectations from a molecular physiology perspective. We illustrate the strong but highly variable effects of elevated CO₂ on root system size and architecture, and provide an update on the signalling mechanisms that may trigger these effects. This highlights the lack of knowledge on the physiological and genetic bases of the root growth and development response to elevated CO₂, but shows that candidate genes and genetic resources are largely available to fill this gap.