Secondary metabolites, carbohydrate accumulation, and nutrient uptake in Aralia elata (Miq.) Seem seedlings exposed to shoot cutting and different LED spectra

Abstract

Aralia elata is a famous homology of traditional medicine and wild vegetable due to its enriched content of flavonoids and saponins. Heavy exploration for shoots has nearly resulted in the exhaustion of the natural reserve of this species, but its traditional culture regime largely depends on land use in the long term. In this study, 1-year-old A. elata seedlings were cultured in commercial substrate under a plant factory condition where lighting was supplied by light-emitting diode (LED) panels in two bionic spectra of 16.9% red (R), 77.8% green (G), and 5.4% blue (B) (R2G4B2) and 12.5% R, 84.6% G, and 2.9% B (R2G10B1) to mimic the understory sunlight in natural populations. An artificial spectrum of 26.6% R, 59.9% G, and 13.5% B (R2G1B3) was also involved as the comparison. All LED lighting had a daily photoperiod of 18 h at the photosynthetic photon flux rate of 150 μmol m−2 s−1. Seedlings were fed by exponential fertilization at the rate of 140 mg nitrogen (N) plant−1[N–phosphorus (P)2O5–potassium (K)2O, 9–30–20]. Shoots were harvested twice with a midway cutting. The R2G10B1 spectrum promoted concentrations of N, P, starch, and total saponins in the secondly harvested shoots, where the R2G4B2 spectrum enhanced stem length, fresh weight, N content, and total saponin content per sprouted shoot. Total flavonoid content had a positive correlation with weight and contents of N, P and sugars, but the positive correlation of total saponins was only with weight. The drastic decline of sprout density in the second harvest decreased the content of total saponins in grouped A. elata seedlings. We conclude that light spectra and shoot cutting had a combined effect on biomass accumulation and total saponins which can be promoted in shoot-cut A. elata seedlings in the R2G4B2 spectrum under plant factory condition.