Responses of Growth, Photosynthetic Physiology, Leaf Microstructural Properties, and Bioactive Compounds of Dendrobium fimbriatum, an Epiphytic Orchid, to Different Light Intensities

Light is a critical ecological factor influencing growth, development, and physiological regulation in epiphytic orchids. To elucidate the adaptive strategies of Dendrobium fimbriatum under different light environments, plants were subjected to three natural light intensity treatments (40%, 20%, and 8% of full sunlight). Growth traits, photosynthetic physiological parameters, leaf microstructural properties, and bioactive compound contents were measured to comprehensively evaluate the response patterns of this species along a light gradient. The results demonstrated that D. fimbriatum does not rely on adjustments of a single trait to cope with changes in light availability; instead, it maintains carbon balance and functional stability through coordinated regulation across growth, physiological, structural, and metabolic levels. Under moderate light conditions (20% light intensity), a high degree of coordination among traits was observed, enabling plants to sustain relatively high photosynthetic efficiency while effectively controlling respiratory consumption and metabolic costs, thereby maintaining elevated carbon assimilation capacity and growth performance. In contrast, under low or relatively high light conditions, plants adopted distinct adjustment pathways to cope with light stress, characterized by enhanced light-use efficiency under low light and strengthened photoprotection and defensive metabolic investment under higher light. These findings indicate that D. fimbriatum can flexibly adjust its growth and physiological strategies in response to changes in light conditions, allowing adaptation to the heterogeneous understory light environment. From the perspective of coordinated multi-trait responses, this study reveals the light adaptation pattern of D. fimbriatum , providing experimental evidence for a deeper understanding of the ecological adaptation mechanisms of epiphytic orchids and offering a theoretical basis for optimizing artificial cultivation practices and light management strategies for this species.