Differences in Morphological and Physiological Responses of Solid and Hollow Petiole Celery Plants to Gradient Shading

Celery production in protected cultivation is frequently subjected to low-light stress. Understanding divergent morphological and physiological responses of celery genotypes to low light is crucial for clarifying the adaptive mechanisms ensuring yield and quality. In this study, two cultivars, solid-petiole celery ‘Ventura’ and hollow-petiole celery ‘Majiagou’ were exposed to full light (CK) and three shading regimes (25%, 50%, and 75% light exclusion). Plant morphological traits, chlorophyll content, gas exchange parameters, activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), soluble protein (SP) and malondialdehyde (MDA) contents were measured. Spearman’s correlation, stepwise regression, and principal component analysis were integrated to comprehensively assess the low-light adaptability of both cultivars. Under 25% and 50% shading treatments, ‘Ventura’ showed smaller reductions in plant height (PH), petiole width (PW), and fresh weight (FW) and increased chlorophyll content, and it maintained a higher net photosynthetic rate. It was also shown that ‘Ventura’ exhibited higher basal SOD level, and a 25% shading treatment rapidly induced coordinated increases in POD and CAT along with SP accumulation, while membrane lipid peroxidation levels changed little. In contrast, ‘Majiagou’ was highly sensitive to low-light conditions. Twenty-five percent shading already caused significant growth inhibition and a sharp photosynthetic decline, with delayed activation of the antioxidant system. Under 50% shading, MDA content in ‘Majiagou’ increased by 196.3% over CK, indicating irreversible membrane damage. Multivariate statistical analysis revealed that biomass accumulation in ‘Ventura’ was driven by net photosynthetic rate, with photosynthesis, osmoregulation, and antioxidation forming a synergistic network. In ‘Majiagou’, biomass depended merely on PH and PW, reflecting weaker physiological adaptability to low light. In summary, ‘Ventura’ exhibits markedly superior shade tolerance and greater suitability for low-light conditions. These findings provide a theoretical basis for cultivar selection and light environment regulation in celery cultivation under insufficient light conditions.