Abstract: We examined the effects of temperature on the leaf gas exchange and chlorophyll fluorescence parameters of two-year-old seedlings of three north highbush blueberry cultivars (Bluecrop, Duke, and Brigitta) in growth chambers. The results showed that the net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), and water use efficiency (WUE) of the three blueberry cultivars shared bellshaped curves with growth temperature, although their maximum values varied with the cultivars. Compared to 25 ℃, intercellular CO₂ concentrations (C_i) of the three cultivars decreased at 30 and 35 ℃, but increased at 40 ℃. Moreover, the results from electrolyte leakage and F_v/F_m demonstrated that the temperatures of 30 and 35 ℃ had little effects on the leaf structure and function, but the temperature of 40 ℃ damaged the cellular membrane structure of blueberry leaves. The temperature of 40 ℃ resulted in severely irreversible damages to both the PSⅡ reaction center structures and electron transport chains. In addition, the three blueberry cultivars had different abilities in resisting heat stress with the order of Brigitta>Bluecrop>Duke. These results may be helpful for further understanding the mechanisms of temperature on the north highbush blueberry cultivars, and provide basis for selection and introduction of heat tolerance cultivars.

Key words: tilt correction, planar fit, energy balance, eddy covariance, triple rotation, double rotation