The Response of Different-Aged Saplings to Light Gradients Reveals New Insights into the Light Requirements of an Endangered Woody Plant Species, Phoebe Chekiangensis

Phoebe chekiangensis is endemic to China and highly valued for art ware, furniture, and timber architecture, having a special status in Chinese history. Natural sources of P. chekiangensis are being depleted, and the species was listed as 'VULNERABLE' on the IUCN Red List of Threatened Species in 1998 (https://www.iucnredlist.org/) due to excessive anthropogenic deforestation and the plant's weak self-regeneration ability. Most studies have attempted to elucidate this weak natural regeneration by culturing seedlings and community surveys, ignoring the different light requirements of seedlings at distinct ages. In this study, we examined five consecutive age groups of seedlings/saplings with current-year (seedling) and 1-4-year-olds exposed to four shading treatments (100%, 40%, 15%, and 5% of full sunlight) for 2 years, based on a randomized complete block design. Using analysis of variance and Duncan's multiple comparison, the growth rate, photosynthetic response, photosynthetic pigments, and ultrastructure of chloroplasts were evaluated among the shading treatments. The results show that the light requirements of P. chekiangensis change during the development process. Moderate shading (40% of full sunlight) is beneficial for the early development of Phoebe seedlings, increasing height growth, photosynthetic efficiency, and photosynthetic pigment content and protecting the development of chloroplast structures. However, full exposure to sunlight is necessary for growing saplings (more than 2 years old) to meet the increased energy demands for growth and development. Overall, this study elucidates P. chekiangensis light utilization during the early regeneration phase, informing seedling cultivation activities and the development of silvicultural strategies of this endangered species.