Effects of melatonin on growth, photosynthesis, and physiological characteristics in Pseudostellaria heterophylla during the late growth stage

Pseudostellaria heterophylla is a traditional Chinese herbal medicine and health food, but its yield of tuberous roots is generally low due to the short effective photosynthetic period. In this study, different concentrations (0, 15, 30, and 45 mg/L) of melatonin (MT) were sprayed on the leaves of P. heterophylla during its late growth stage to investigate the effects of MT on the growth, photosynthesis and physiological characteristics. The results showed that most growth indicators increased with the elevation of MT concentration. The fresh root yield in M3 (45 mg/L) was 25.61 % higher than that in CK (0 mg/L); while the contents of polysaccharides and saponins in tuberous roots also increased by 34.21 % and 66.48 %, respectively. Compared with CK, MT treatments improved the net photosynthetic rate, stomatal conductance, and transpiration rate to varying degrees, with the M3 of the best effects. The photoinhibition caused by leaf senescence was also effectively alleviated in M3, which decreased non-photochemical quenching and enhanced the photochemical efficiency. Notably, changes of specific energy fluxes (TR 0 /CS m , ET 0 /CS m , DI 0 /CS m ) by JIP-test in M3 were basically consistent with the corresponding quantum yields (φP 0 , φE 0 , φD 0 ), and the photosynthetic performance index was 209.60 % higher than that of CK. These combined results eventually led to a significant accumulation of the primary photosynthetic products. Moreover, MT treatments also altered the redox modulation, which inhibited the production of reactive oxygen species and the decline in chlorophyll contents. To summarize, MT delayed leaf senescence and improved the photosynthetic activity of P. heterophylla in the late growth stage, ultimately promoting a comprehensive improvement in yield and quality. • The application of Melatonin (MT) in the late growth stage of Pseudostellaria heterophylla increases the yield and quality. • MT increases the photosynthetic capacity of P. heterophylla in the late growth stage by enhancing photosynthetic apparatus activity. • MT delays leaf senescence of P. heterophylla in the late growth stage by modulating REDOX homeostasis.