The physiological and molecular responses of Ophiopogon japonicus to drought and waterlogging stresses at two growth stages

Abstract The growth and medicinal quality of Ophiopogon japonicus are susceptible to water stress, yet little is known about how drought and waterlogging differentially regulate physiological and molecular responses across developmental stages. This study conducted pot experiments during the vegetative growth stage (September–October) and tuberous root expansion stage (January–February), applying drought (soil water content maintained at 15%, w/w) and waterlogging (2–3 cm water layer above soil surface) for 3, 6, 12, and 24 days, with three biological replicates per treatment. Growth, yield, quality, antioxidant enzyme activities, membrane lipid peroxidation, osmolytes, and endogenous hormone levels were measured, and transcriptome profiling was performed at the 12-day time point. The results revealed significant stage- and organ-specific responses: during the vegetative stage, drought strongly inhibited root growth and activated antioxidant defense and osmotic adjustment, whereas short-term waterlogging slightly promoted growth and long-term waterlogging was mildly inhibitory; during the tuberous root expansion stage, short-term stress promoted dry matter accumulation whereas prolonged stress reduced yield, and ABA was prominently associated with drought response. Final harvest analysis showed that early drought inhibited shoot and fibrous root growth but promoted tuberous root yield, with opposite patterns for waterlogging; drought during the tuberous root expansion stage increased polysaccharide and methylophiopogonanone A/B contents, whereas waterlogging reduced quality. Transcriptome analysis suggested that drought-induced quality improvement was associated with enrichment of phenylpropanoid biosynthesis, whereas waterlogging-induced yield and quality decline was associated with altered secondary metabolism and lipid metabolism pathways. This study demonstrates that O. japonicus dynamically adjusts physiological strategies according to growth stage, providing insights for precision water management.