Impacts of abiotic stresses on cotton physiology and vigor under current and future CO₂ levels

Elevated CO₂ (eCO₂) may mitigate stress-induced damage to cotton (Gossypium spp.) growth and development. However, understanding the early-stage responses of cotton to multiple abiotic stressors at eCO₂ levels has been limited. This study quantified the impacts of chilling (CS, 22/14°C, day/night temperature), heat (HS, 38/30°C), drought (DS, 50% irrigation of the control), and salt (SS, 8 dS m^–1) stresses on pigments, physiology, growth, and development of 14 upland cotton cultivars under ambient CO₂ (aCO₂, 420 ppm; current) and eCO₂ (700 ppm; future) levels during the vegetative stage. The eCO₂ partially negated the effects of all stresses by improving one or more of the pigments, physiological, growth, and development traits, except CS. For instance, HS at aCO₂ significantly increased stomatal conductance by 36% compared with non-stressed plants at aCO₂. However, HS at eCO₂ significantly decreased stomatal conductance by 18% compared with HS at aCO₂. The first squaring was delayed by one day under SS at aCO₂ but two days earlier under SS at eCO₂ than non-stressed plants at aCO₂. Root and shoot dry mass and the total leaf area were significantly higher under all stresses, except for CS, at the eCO₂ compared with similar stresses at the aCO₂. Most growth and development traits, including plant height, leaf area, and shoot dry mass, displayed a mirroring response pattern between aCO₂ and eCO₂ under all environments except CS. Cultivars exhibited significant interaction with stressed environments. Further, results revealed differential sensitivity and adaptation potential of cultivars to stress environments at varying CO₂ levels. This study highlights the need to consider eCO₂ in designing breeding programs to develop stress-tolerant varieties for future cotton-growing environments.