Abstract:The seasonal changes in photosynthetic characteristics of three deciduous broad-leaved species (Fagus lucida, Acer davidii, and Liquidambar acalycina) and four evergreen broad-leaved species (Castanopsis lamontii, Cyclobalanopsis oxyodon, Manglietia chingii, and Schima argentea) in Guangxi Mao’er Mountain were studied. Except of Acer davidii, there was not significant difference in maximum photosynthetic rate at saturating light (Pmax) between the deciduous and evergreen species, but maximum stomatal conductance at saturating light (Gmax) was higher in the deciduous species than the evergreen species in rainy season. However, in dry season, the decreases of Pmax and Gmax were greater in the deciduous species than the evergreen species, as accompanied by the larger increases in dark respiration rate and light compensation point in the former. The deciduous and evergreen species had slight difference in apparent quantum yield (AQY) and predawn maximum photochemical efficiency of photosystem II (Fv/Fm-predawn) in rainy season. However, in dry season, the deciduous species showed lower AQY and Fv/Fm-predawn than the evergreen species, suggesting that the deciduous species suffered greater photoinhibition. Furthermore, there was a significant linear relationship between P and G, and the evergreen species showed lower slope, indicating that the evergreen species had higher photosynthetic water use efficiency and this would help them to survive in dry and cold conditions. Also, the significant linear correlations of P with electron transport rate and leaf temperature were observed in both the deciduous and evergreen species, and the evergreen species exhibited lower slope; this indicates that the evergreen species could adjust the electron transport rate through alternative electron pathways to adapt to the wide range of seasonal temperatures. In conclusion, the results obtained here suggest that the deciduous species required relatively higher temperature and water supply than the evergreen species to meet the needs of photosynthesis; under dry and cold situations, it’s therefore unavoidable for them to suffer greater photoinhibition and shed their leaves finally, although the coordinated adjustments in stomata and photosystem II occurred in them. By contrast, the evergreen species could adapt to dry and cold stresses and maintain green leaves by promoting photosynthetic water use efficiency through stomatal control and dissipating excessive light energy via electron allocation.
