Exploring the responses of crop photosynthesis to CO2 elevation at the molecular, physiological, and morphological levels toward increasing crop production

Exploring the impact of elevated CO₂ on photosynthesis is vital for understanding plant responses to climate change. In C₃ plants, elevated CO₂ concentrations generally enhance CO₂ assimilation by increasing chloroplast CO₂ concentration. However, the underlying mechanisms are complex since photosynthesis involves multiple physiological processes operating at different time scales and varying among plant species. In this review, we focused on the responses of key photosynthetic processes in crop, including CO₂ diffusion conductances such as stomatal conductance (g_s), mesophyll conductance (g_m), photochemical reactions, the Calvin-Benson cycle, and related metabolic pathways. Short-term exposure to elevated CO₂ often decreases g_s and g_m while increasing the electron transport rate. However, long-term exposure to elevated CO₂ can decrease photosynthetic capacity due to coordinated downregulation of multiple processes, particularly when the sink‒source ratio declines. To enhance plant productivity under elevated CO₂, it is crucial to maintain or enhance sink activity and understand the CO₂ response mechanisms at the molecular, physiological, and morphological levels. This review provides an update on the short- and long-term responses of g_s, g_m, electron transport system, and carbon assimilation metabolism to elevated CO₂. Furthermore, it offers a perspective on improving crop production in the future with elevated CO₂ levels.