Abstract: [Objective]This study aimed to explorethe relationships between leaf morphological structure, photosynthetic characteristics and water physiological characteristics, and the internal causes affecting plant biomass accumulation of Populus euramericana cv. ‘BYu’ in comparison with P. popularis ‘35-44’ and further reveal the drought-resistant of P.euramericana cv.‘BYu’ and P. popularis ‘35-44’, which could lay foundations for the drought physiology research and the promotion of poplar varieties in regional afforestation.[Method]A pot experiment with one-year-old cuttings of P.popularis ‘35-44’ and P.euramericana cv.‘BYu’ was conducted to investigate the effect of different drought stress on leaf area (LA), leaf vein density (LVD), leaf nitrogen use efficiency, photosynthetic characteristics and leaf hydraulic conductance(LHC), and their influence on plant biomass accumulation and drought-resistant ability.[Result]With the increase of drought stress, LVD and leaf nitrogen content per mass(N_mass) of two poplar varieties increased, and LVD increased more and N_mas increased less for P.euramericana cv.‘BYu’.Net photosynthetic rate(P_n), photosynthetic rateper plant(PTL),maximum net photosynthetic rate (P_nmax),daily accumulation of P_n and Tr, K_leaf, water use efficiency(WUE), photosynthetic nitrogen use efficiency(PNUE), LA and plant total biomass(TB) all decreased, with decreased less for P.euramericana cv.‘BYu’.Compared with P.popularis ‘35-44’, P.euramericana cv.‘BYu’ had higher LA, LVD, PNUE, TB,and daily water consumption, lower P_n, K_leaf, WUE, N_mass before and after drought stress, higher PTL, P_nmax, and daily accumulation of Tr under moderate and severe drought stress,and higher P_nmax, daily accumulation of P_n, and Tr under severe drought stress. PTL was more closely related to TB than P_n, and, PNUE was more closely related to than N_mass.[Conclusion]Under drought stress, the leaf morphological structure and physiological characteristics of P.euramericana cv.‘BYu’ presented a balanced constraint relation between inefficient water utilization, efficient adjustment of leaf morphological structure, efficient nitrogen utilization, efficient assimilation of carbon.Drought resistance mechanism of these two varieties wasdifferent, P.euramericana cv.‘BYu’ with strong drought-resistancehad more efficient leaf structure adjustment, P.popularis ‘35-44’ with weak drought-resistancehad more sensitive photosynthetic characteristics to drought. Leaf structure was most associated with drought resistance, followed by photosynthetic characteristics.

Key words: Populus euramericana cv. ‘BYu’, drought stress, leaf morphological structure, photosynthetic characteristic, water physiological characteristic, plant biomass