Effects of Seasonal Changes on Chlorophyll Fluorescence and Physiological Characteristics in the Two Taxus Species

Taxus is a rare and endangered woody plant worldwide with important economic and ecological values. However, the weak environmental adaptability of Taxus species, in particular the unstable photosynthetic activity in different seasons, always affects its normal growth and development and limits its conservation and exploitation. To improve the survival of Taxus trees in cultivated areas, the seasonal dynamics of chlorophyll fluorescence (CF) and key physiological parameters were comprehensively investigated in T. media and T. mairei. The results demonstrated that the photosynthetic activity of both Taxus species was sensitive to local summer and winter environmental conditions, with the heterogeneity of fluorescence signatures intuitively presented on the needle surface by CF-Imaging detection, while images of maximum quantum efficiency of PSII photochemistry (Fv/Fm) demonstrated values below 0.7 in the blue–green sectors in winter. The distribution of light energy was regulated by the photosynthetic apparatus in both Taxus species to maintain a stable actual quantum yield of PSII photochemistry (φPSII), which was around 0.4–0.5. Based on a redundancy discriminant analysis, the interpretation rate of light intensity and air temperature ranked as the top two in both Taxus species, which were considered the main environmental factors affecting the photosynthetic performance of Taxus by disturbing the electron transport chain. In the winter, T. mairei exhibited weaker electron transport activity than T. media, thus caused lower photochemistry and more severe photosynthetic damages. Interestingly, both Taxus species demonstrated consistent response patterns, including diverse energy dissipation strategies and enhancement of osmoregulatory substances and antioxidative activities, thus maintaining stable photosynthetic functions in response to environmental changes.