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 mu mol 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 (phi PSII), potential quantum efficiency of PSII (F-v/F-m), actual PSII efficiency (Delta 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 phi PSII 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.

Automated summary

The study aimed to measure the chlorophyll fluorescence (ChlF) parameters of Barbula indica and Conocephalum conicum under different light intensities (LI) to understand their adaptability to their habitats. The results showed that the electron transport rate (ETR) of all plants was highest under 500 PPFD conditions, indicating their optimal growth under specific light intensity. As LI increased, non-photochemical quenching (NPQ) and photo-inhibitory quenching (q(I)) increased, while photosystem II efficiency (phi PSII) and potential quantum efficiency of PSII (F-v/F-m) decreased in all plants. Energy-dependent quenching (q(E)), the light protection system (q(E) + q(Z) + q(T)), and q(I) increased under higher LI, suggesting higher photo-protective ability in these plants. Barbula indica remained photochemically active, while Conocephalum conicum exhibited higher photo-protection under certain LI conditions. These ChlF parameters can be used to predict photosynthetic responses in different bryophytes and contribute to ecological monitoring.