Physiological and stomatal trait responses of Raphanus sativus cultivars under elevated CO2

Elevated atmospheric CO 2 (eCO 2 ) will reshape crop physiology, yet genotypic differences in responsiveness remain poorly resolved. We compared nine Raphanus sativus cultivars grown at 400, 800 and 1200 ppm CO 2 to quantify coordinated changes in leaf gas exchange, pigment composition and stomatal traits. Across cultivars, CO 2 enrichment significantly increased net assimilation ( P < 0.05) while stomatal conductance declined and intercellular CO 2 rose. Chlorophyll a and b increased with CO 2 , and zeaxanthin generally accumulated, whereas β -carotene changed only slightly, revealing cultivar-dependent reallocation within the photosynthetic pigment system. Stomatal density responded in a genotype-specific manner, increasing in several cultivars but remaining stable or decreasing in others, highlighting plasticity in epidermal patterning under CO 2 enrichment. Parallel-analysis PCA identified a single dominant axis integrating assimilation (C i ), pigments, and stomatal traits, with elevated CO 2 shifting cultivars toward higher PC1 scores. Several traits showed significant CO 2 x cultivar interactions, confirming differential responsiveness among genotypes. Together, these results identify cultivars differing in CO 2 -driven physiological responsiveness and trait coordination under elevated CO 2 .