Atmospheric CO 2 concentrations are rising and projected to reach ∼800 μmol mol -1 by 2100, while soil salinity is expanding globally, yet their combined impact on crops remains unclear. In particular, the interactive effects of elevated CO 2 and salinity on maize ( Zea mays L.) physiology and development are poorly understood. The physiological and anatomical responses of maize to elevated CO 2 (800 μmol mol -1 ) and NaCl stress (0-150 mmol L -1 ) were investigated through a controlled factorial experiment. Results showed that elevated CO 2 increased net photosynthetic rate, water-use efficiency, and biomass accumulation, partially mitigating salt-induced reductions in growth and photosynthesis under moderate NaCl stress, while mitigating salt-induced growth inhibition through three key mechanisms: (1) reinforcement of antioxidant defenses and improve water use efficiency by upregulating superoxide dismutase and peroxidase, (2) osmotic adjustment via leaf non-structural carbon accumulation especially under moderate salinity, and (3) high salinity caused structural deteriorations such as thinner leaves, lower stomatal density, and reduced vascular bundle size, while elevated CO 2 counteracted salinity-induced structural degradation, maintaining leaf thickness and vascular bundle integrity while modulating stomatal patterning and opening. However, growth and physiological function were still markedly hindered under severe salinity. Our multi-trait analysis demonstrates that rising CO 2 may partially compensate for salinity impacts in maize, providing critical insights for predicting C 4 crop stress resistance under future climate scenarios. • Elevated CO 2 boosted photosynthesis and WUE, reducing growth loss under salinity • Spatial analysis shows elevated CO 2 alters stomatal distribution in maize leaves • Elevated CO 2 may offset salt stress in maize, boosting resilience to future climates
Ma et al. (Wed,) studied this question.