Photosynthetic Response to Irradiance in Valeriana jatamansi Jones, a Threatened Understorey Medicinal Herb of Western Himalaya

Net photosynthetic rate (PN) of Valeriana jatamansi plants, grown under nylon net shade or under different tree canopies, was saturated with photons at 1 000 μmol m-2 s-1 photosynthetic photon-flux-density (PPFD), whereas open-grown plants were able to photosynthesise even at higher PPFD, e.g. of 2 000 μmol m-2 s-1. Plants grown under net shade had higher total chlorophyll (Chl) content per unit area of leaf surface. However, Chl a/b ratio was maximal in open-grown plants, but remained unchanged in plants grown in nylon net shade and under different tree canopies. Sun-grown plants had thicker leaves (higher leaf mass per leaf area unit), higher wax content, and higher PN than shade grown plants. Thus V. jatamansi is able to acclimate to high PPFD and therefore this Himalayan species may be cultivated in open habitat to meet the ever-increasing industrial demand.