Photo-protection and photo-inhibition during light induction in Barbula indica and Conocephalum conicum under different light gradients

The objectives of this study were to measure the chlorophyll fluorescence (ChlF) parameters of Barbula indica (Hook.) Spreng and Conocephalum conicum (L.) Dumort subjected to various light intensities (LI) as a reflection of their adaptability to their habitats. The electron transport rate (ETR) of all plants under 500 μmol m –2 s –1 photosynthetic photon flux density (PPFD) was significantly higher than other LI treatments, implying that these plants could be grown under a specific and optimal light intensity adapted to 500 PPFD conditions. As LI increased from 50 to 2,000 PPFD, we observed in all plants increased non-photochemical quenching (NPQ) and photo-inhibitory quenching ( q I ) and decreased photosystem II efficiency (ΦPSII), potential quantum efficiency of PSII ( F v / F m ), actual PSII efficiency (Δ F / F m ′%), and F v / F m %. In addition, energy-dependent quenching ( q E ), the light protection system ( q E + q Z + q T ), and q I increased as ΦPSII decreased and photo-inhibition% increased under 1000, 1500, and 2000 PPFD conditions, suggesting that these plants had higher photo-protective ability under high LI treatments to maintain higher photosynthetic system performance. B. indica plants remained photochemically active and maintained higher q E under 300, 500, and 1000 PPFD, whereas C. conicum q Z + q T exhibited higher photo-protection under 500, 1000, and 1500 PPFD conditions. These ChlF indices can be used for predicting photosynthetic responses to light induction in different bryophytes and provide a theoretical basis for ecological monitoring.