Abstract: To explore the photosynthetic physiological characteristics of greening tree species and understand the mechanisms of photosynthetic physiological adaptation of plants in different seasons in the central Loess Plateau, photosynthetic response curve and diurnal variation of three typical tree species (Prunus sibirica, Robinia pseudoacacia andPopulus alba) in different seasons were measured using Li6400XT portable photosynthetic instrument. The results showed that: (1) The diurnal variation of net photosynthetic rate (P_n) ofP. sibirica andR. pseudoacacias showed a single peak curve, while that of P. alba showed an asymmetric double peak curve. (2) P. sibirica, R. pseudoacacia,and P. alba had higher maximum photosynthetic rate (8.29, 8.79, 12.94 μmol·m^-2·s^-1) in summer, and higher apparent quantum efficiency (0.058,0.032, 0.073 μmol·μmol^-1), lower light compensation point (8.69, 3.44, 4.72 μmol·m^-2·s^-1) and dark respiration rate (0.48, 0.11, 0.33 μmol·m^-2·s^-1) in autumn. There were significant seasonal variations in light saturation point. (3) Water use efficiency of P. sibirica and R. pseudoacaciawas higher in autumn (1.97, 4.66 μmol·mmol^-1), but that ofP. alba was higher in summer (7.29 μmol·mmol^-1). (4) P. alba had higher net photosynthetic rate and water use efficiency, with a wide range of light adaptation. R. pseudoacacia had a strong ability to use strong light, but with moderate water use efficiency. P. sibirica had higher shade tolerance and lower water use efficiency. (5) Results of path analysis showed that, relative humility (RH), soil temperature (T_s) and air temperature (T_a) all inhibited P_n of the three species in spring. The abovementioned environmental factors showed similar effects on apricot and R. pseudoacacia in summer to that in spring. The four environmental factors examined here promoted the P_n of P. alba; in autumn. P_n of the three species was positively promoted by T_s but inhibited by PAR, RH and T_a. In general, those three tree species showed a positive growth pattern with seasonal changes, among which the adaptability of P. alba was stronger than that of P. sibirica and R. pseudoacacia. Our results provide theoretical basis for the introduction, cultivation, and application of afforestation tree species in arid and semi-arid areas.

Key words: Northern Mountain of Lanzhou, greening tree species, diurnal variation of photosynthesis, physiological parameter, path analysis.