Abstract: In this study, seven typical temperate tree species were used as examples to establish vulnerability curve (VC) of water potential and xylem loss (PLC) by natural drying method. Continuous soil drought treatment was carried out on the tree species under controlled conditions to analyze plant gas exchange and photochemical parameters at the point of control, moderate drought (50% PLC water potential) and severe drought conditions (80% PLC water potential). The sequence of vulnerability to xylem embolism of 7 species was followed by Quercus acutissima, Abies holophylla Maxim., Populusnigra, Picea asperata Mast., Sequoia sempervirens, Acer palmatum and Cyclobalanopsis glauca. The embolization VC curve of Populusnigra was “S” type, while the other 6 species’ were “R” type. Under moderate and severe drought stress, photosynthetic rate and PSII activity were decreased significantly. Cyclobalanopsis glauca, Sequoia sempervirens, Populusnigra and Quercus acutissima were tested as isohydric species, Picea asperata Mast. was tested as intermediate species, Acer palmatum and Abies holophylla Maxim. were tested as anisohydric species. Result showed that the water regulation pattern of these different trees had little relationship with embolism resistance and drought resistance. Drought resistance experiments based on PLC could clearly reflect the interspecific differences in water regulation and drought tolerance, and help us clarify the survival mechanism of trees to moderate or higher drought stress. Interspecific analysis showed that intercellular CO2concentration (not Fv′/Fm′) had a consistent response to the degree of xylem embolization, which could be used as a predictor of embolization under drought condition.

Key words: vulnerability curves, xylem embolisms, isohydric species, anisohydric species, chlorophyll a fluorescence