Photosynthetic acclimation of crassulacean acid metabolism orchid Phalaenopsis in response to light level

Phalaenopsis orchids exhibit remarkable photosynthetic plasticity, enabling them to effectively acclimate crassulacean acid metabolism (CAM) to a wide range of light levels. Herein, the photosynthetic acclimation of Phalaenopsis Queen Beer 'Mantefon' was examined under different light intensities. Phalaenopsis clones grown under a photosynthetic photon flux density (PPFD) of 100 µmol m^-2 s^-1 were subjected to different light intensities of 10, 50, 100, and 200 µmol m^-2 s^-1 for either one day or two months of modified light levels, and their chlorophyll fluorescence response and CO₂ exchange rate were observed. The electron transport rate (ETR) varied rapidly to changing light levels, showing a significant positive correlation with light intensity after just one day of treatment. Only plants exposed to an elevated light intensity of 200 µmol m^-2 s^-1 for 1 day showed a decrease in ETR after midday. Moreover, after 2 months, the ETR decreased more slowly under 200 µmol m^-2 s^-1. Long-term exposure to varying light conditions for two months led to increased CO₂ uptake, even at reduced light intensities. The plants also exhibited an enhanced malic acid recovery rate under both low- and high-light conditions. Citric acid levels also varied with light intensity. High-light conditions led to a significant increase in plant growth, characterized by greater biomass and a higher number of leaves. Furthermore, stable carbon isotope analysis revealed differences in the daytime CO₂ uptake rate of Phalaenopsis plants grown under different light intensities for two months. In this manner, Phalaenopsis orchids exhibit remarkable plasticity in their photosynthetic pathways, allowing them to acclimate effectively to different light environments. Investigating Phalaenopsis light acclimation is crucial for understanding the mechanisms underlying photosynthetic optimization and growth in diverse light environments in CAM plants.