Abstract: The LI-6400 portable photosynthetic instrument （LI-COR,USA） was used to measure the photosynthetic physiological parameters of Populus euphratica growing in the extreme arid area along the Tarim River. Based on the analysis of the dynamic changes of the intercellular CO₂ concentration of P. euphratica, the stomata limitation and non-stomata limitation of P. euphratica were further discussed and explored. The results showed, the intercellular CO₂ concentration of P. euphratica leaves in the growing season showed a “V”-shaped change trend, and the lowest values ??all appeared at 14：00. The intercellular CO₂ concentration of P. euphratica changed synchronously with changes in influencing factors including external CO₂ concentration, stomatal conductance, net photosynthetic rate and transpiration rate：it was basically consistent with the change law of external CO₂ concentration; It was opposite to the change law of stomatal conductance, net photosynthetic rate and transpiration rate, showing a negative correlation. The change law of the stomatal limit value L_s of P. euphratica leaves showed a trend of first increasing and then decreasing, which was lower in the morning and evening and higher at noon. The non-stomata limitation index C_i/G_s and stomata limitation L_s change in the opposite way. The decline of P. euphratica net photosynthesis rate was mainly due to non-stomata limitation, but the effect of stoma limitation cannot be ruled out. Similarly, when the net photosynthesis rate decline was mainly due to non-stomata limitation, it cannot be ruled out. Combining the two judgment basis of stomata limitation value L_s and non-stomata limitation can further understand P. euphratica stoma limitation and non-stomata limitation.

Key words: Populus euphratica Oliv., intercellular CO₂ concentration, photosynthesis, stomatal limitation, non-stomatal limitation