Light energy partitioning and photoprotection from excess light energy in shade-tolerant plant Amorphophallus xiei under steady-state and fluctuating high light

Light is the most essential environmental factor that plants require for the growth and development. However, light is highly heterogeneous in natural condition, and plants have to evolve a series of strategies to acclimate the dynamic light since it is sessile. The photosynthetic performance and regulatory mechanisms involved in acclimation were elucidated in shade-tolerant plant Amorphophallus xiei under steady state and fluctuating high light. The dissipation and allocation of light energy, photosynthetic capacity, and antioxidant defense were examined in A. xiei cultivated under 4%, 17%, and 100% of full sunlight. High-light-grown plants exhibited reduced photosynthesis and the slowest response to simulated sunflecks than the other two treatments. Maximum and actual efficiency of PSII photochemistry ( F v ′/ F m ′ and Φ PSII ) and electron transport rate (ETR) were lowest, and non-photochemical quenching (NPQ) were highest in high-light-grown plants than in low- and intermediate-light-grown plants subjected to different photon flux densities (PFD) and intercellular CO 2 concentrations ( C i ). F v ′/ F m ′, Φ PSII , ETR and NPQ were lowest in high-light-grown A. xiei than others, when plants were exposed to simulated sunflecks. In fully light-induced leaves, high-light-grown plants showed a maximum value in quantum efficiency of light-dependent thermal dissipation (Φ NPQ ), and a minimum value in Φ PSII was recorded. Low-light-grown plants subjected to simulated sunflecks, a maximum value in Φ NPQ and Φ PSII were observed. Mass-based nitrogen content ( N area ), specific leaf area (SLA), superoxide dismutase (SOD) and catalase (CAT) activities significantly declined with the increase of growth irradiance. The high-light-grown plants showed higher xanthophyll de-epoxidation and ascorbate–glutathione cycle activity, while low-light-grown plants showed higher neoxanthin and β -carotene contents. In general, high-light-grown A. xiei generally show a depressed photosynthetic capacity, and are efficient in dissipating excess light energy by NPQ under a steady-state light but not under a highly fluctuating light. Low-light-grown plants show a rapid photosynthetic assimilation response to sunflecks and then a rapid activation of the energy-dependent quenching (qE) component of NPQ under the sunflecks. In addition, high-light-grown plants, although using various strategies to reduce light absorption and to scavenge reactive oxygen species , have less efficient protection against photodamage.