Morphological and Photosynthetic Response to High and Low Irradiance of Aeschynanthus longicaulis

Aeschynanthus longicaulis plants are understory plants in the forest, adapting to low light conditions in their native habitats. To observe the effects of the high irradiance on growth and physiology, plants were grown under two different light levels, PPFD 650 μmol·m(–2) ·s(–1) and 150 μmol·m(–2) ·s(–1) for 6 months. Plants under high irradiance had significantly thicker leaves with smaller leaf area, length, width, and perimeter compared to the plants grown under low irradiance. Under high irradiance, the leaf color turned yellowish and the total chlorophyll decreased from 5.081 mg·dm(−2) to 3.367 mg·dm(−2). The anthocyanin content of high irradiance leaves was double that of those under low irradiance. The plants under high irradiance had significantly lower A(max) (5.69 μmol·m(–2) ·s(–1)) and LSP (367 μmol·m(–2) ·s(–1)) and higher LCP (21.9 μmol·m(–2) ·s(–1)). The chlorophyll fluorescence parameter F (v)/F (m) was significantly lower and NPQ was significantly higher in high irradiance plants. RLCs showed significantly lower ETR(max⁡) and E (k) in plants under high irradiance. It can be concluded that the maximum PPFD of 650 μmol·m(–2) ·s(–1) led to significant light stress and photoinhibition of A. longicaulis.