Winter leaf reddening is a phenomenon that evergreen species’ leaf colour changes into red before or during winter, which persists for several months before dissipating with springtime warming. To better understand whether the Photoprotection mechanism triggers this phenomenon, we utilized the photochemical reflectance index (PRI) as a tool to reflect the photosynthetic activities. The digital camera was used to monitor the canopy phenology changes. The RGB channels of image data were extracted to calculate the Red-Green vegetation index (RGVI) to track the colour changes of leaves. The CO2 flux data and the micrometeorological data were also collected.
Our findings demonstrated that the one-month lag between Ta and PAR reach their minimum might cause an imbalance between light energy absorption and utilization, which might activate the photoprotection mechanism. The light use efficiency (LUE) reached its peak at the end of December then dropped sharply might confirm this conjecture. The RGVI fluctuation showed the seasonal changes with that of PRI almost in contrast. PRI was highly correlated with RGVI (R=-0.807, p<0. **), which suggested that the winter leaf reddening phenomenon caused the decline of PRI. Further, the sunny day PRI and RGVI were both highly correlated with Ta and PAR.