Abstract: The CI-340 Portable Photosynthesis System and WatchDog 2000 Weather Station were employed to measure the photosynthesis of Platycladus orientalis L., Caragana korshinskii Kom. and Tamarix austromongolica Nakai in the Beishan Mountain of Lanzhou. The influencing factors of photosynthesis were observed and analyzed by path analysis. The results showed that: (1) The main physiological determinant factors were different among the three plants: transpiration rate for P. orientalis, intercellular CO₂ concentration for C. korshinskii and leaf temperature for T. austromongolica. There were also obvious distinctions in the main physiological limiting factors among the three plants: leaf temperature for P. orientalis and C. korshinskii, and transpiration rate for T. austromongolica. (2) The three plant species differed in determinant environmental factors affecting their photosynthesis. Photosynthetically active radiation was the major environmental determinant for P. orientalis, and air relative humidity for C. korshinskii and T. austromongolica. However, soil moisture was the major environmental limiting factor for P. orientalis and T. austromongolica, and atmospheric CO₂ concentration for C. korshinskii.

Key words: plant growth promoting, Bacillus, microflora