Photosynthetic responses of Eulophia dentata, Bletilla formosana, and Saccharum spontaneum under various photosynthetic photon flux density conditions.

This study aimed to determine the photosynthetic performance and differences in chlorophyll fluorescence (ChlF) parameters between Eulophia dentata and its companion species Bletilla formosana and Saccharum spontaneum when subjected to different photosynthetic photon flux density (PPFDs). Leaf surfaces were then illuminated with 50, 100 (low PPFDs), 300, 500, 800 (moderate PPFDs); 1,000; 1,500; and 2,000 (high PPFDs) μmol m^-2·s^-1, and the ChlF parameters were measured during the whole process. Increasing nonphotochemical quenching of ChlF and decreasing potential quantum efficiency of PSII, actual quantum efficiency of PSII, and quantum efficiency ratio of PSII in dark recovery from 0-60 min were observed in all leaves. A significant and negative relationship was detected between energy-dependent quenching (q_E) and photoinhibition percent in three species under specific PPFD conditions, whereas a significant and positive relationship was detected between photoinhibitory quenching (q_I) and photoinhibition percent. The q_E and q_I can be easily measured in the field and provide useful ecological indexes for E. dentata species restoration, habitat creation, and monitoring.