Seasonal Variations in the Growth and Physiology of Acer miaotaiense subsp. yangjuechi Fang et P. L. Chiu Seedlings Under Shading Treatments

This study investigated the seasonal variations in photosynthetic characteristics and adaptation mechanisms of the endangered Acer miaotaiense subsp. yangjuechi Fang et P. L. Chiu under different shading treatments, offering theoretical insights and technical support for its relocation and conservation strategies. Five shading intensity treatments were established: full light (CK), 30% (T1), 50% (T2), 70% (T3), and 90% (T4). The growth and physiological conditions of 5-year-old A. miaotaiense subsp. yangjuechi seedlings were monitored across seasons. The findings revealed that plants grown under 70% shade had the best growth performance and leaf morphological indices. In summer, the levels of osmotic adjustment substances and peroxidase activity were the highest, whereas malondialdehyde (MDA) levels increased progressively throughout the season. Notably, superoxide dismutase activity exhibited an opposite trend to MDA. Proline and MDA contents were the highest under full light conditions and lowest under 70% shade, whereas soluble sugars and starch showed the reverse pattern. Chlorophyll content and photosystem II efficiency peaked under 70% shade, with the highest net photosynthetic rate and light saturation point observed in the 70% and 90% shade treatments. A comprehensive evaluation suggests that 70% shade is more conducive to the normal growth and development of A. miaotaiense subsp. yangjuechi seedlings.