Elevated CO₂ improves lodging resistance of rice by changing physicochemical properties of the basal internodes

Elevated atmospheric CO₂ concentration has been shown to increase rice yield but its effect on plant lodging resistance is still under debate. In this study, we examined lodging incidence in the field and lodging-related traits of two rice cultivars with contrasting lodging susceptibility under ambient and elevated CO₂ (ca. 200 μmol mol^-1 above ambient) concentrations by using a free-air CO₂ enrichment (FACE) system. Elevated CO₂ (E-CO₂) increased lodging resistance as shown by reduced visual lodging incidence in the field at the late grain filling stage in E-CO₂ plots. This coincided with enhanced in situ pushing resistance of intact plants one week before lodging occurred. The positive CO₂ effect was more pronounced in the lodging-susceptible cultivar LY084. In contrast, the cultivar WYJ23 displayed greater pushing resistance in the field, and no lodging occurred at either ambient or elevated CO₂ conditions throughout the cropping season. The field observations were consistent with the physicochemical characterization of basal internodes of rice plants at the grain filling stage. Greater lodging-resistance of WYJ23 was mainly attributed to its shorter plant height and thicker culm wall of basal internodes. The improvement of lodging resistance by E-CO₂ for the lodging-susceptible cultivar LY084 was mainly related to enhanced culm density, which was explained by elevated starch deposition in the stem. Less lodging incidence under elevated CO₂ contributed to an increase in grain yield by 36% for LY084. In conclusion, rice production could benefit from elevated CO₂ in a changing climate because of an increase in lodging resistance as a result of CO₂-induced improvements in mechanical strength of basal internodes.