Abstract: We compared the interspecific and intraspecific clonal growth and photosynthetic physiology ofPopulus euphraticaOliv. and Populus pruinosa Schrenk in the mixed forest in different groundwater-level habitats in Alar, Xinjiang, China. Under the same habitat, Populus euphraticaand Populus pruinosa differed in leaf area and dry weight of ramets. The leaf area and leaf dry weight of Populus pruinosa were significantly higher than those of Populus euphratica, while the net photosynthetic rate, stomatal conductance, transpiration rate and CO₂ utilization efficiency of the ramets of Populus pruinosa were significantly higher than those of Populus euphratica. Across different habitats, basal diameter, plant height, leaf number, leaf area, stem dry weight and leaf dry weight of each clump of the ramets of both species were significantly higher in the habitat of 1.5 m groundwater level than in the habitat of 2.6 m groundwater level, whereas the number of branches per clump and the specific leaf area were opposite. The stomatal conductance, intercellular CO₂ concentration, net photosynthetic rate, and water use efficiency of Populus euphratica ramets in the habitat with low groundwater level were significantly higher than those in the habitat with high groundwater level. Collectively, under the same habitats, Populus pruinosa ramets had a stronger ability to acquire light resources than Populus euphratica ramets. Under different habitats, the differences in the growth and photosynthetic physiological characteristics in both Populus euphratica and Populus pruinosa ramets were related to groundwater depth.

Key words: mixed forest, ramet, growth characteristics, photosynthetic physiology.