中文摘要：

本研究以毛果杨、毛白杨、银灰杨、欧美杨和胡杨为研究对象，对其苗期生长、光合作用、微观结构、木质素组成、激素含量等多个指标进行分析比较，旨在寻找其苗期生长和生理特征上的差异，探究不同杨树生长速度不同、应用不同的原因，进而指导应用。研究发现毛白杨、银灰杨和欧美杨表现出栽后缓苗迅速、生长速度快的特点。可能是受到较强光合作用（有机物合成积累）和较强蒸腾作用（水和元机盐的运输）双重因素的影响，即光合速率高、光合能力强，能合成积累更多有机物；气孔导度值较高、蒸腾速率高，能够有效吸收CO2进行光合，并且能高效运输水和无机盐，在生产应用中具有很大潜力。毛白杨的木质素含量高，适于建筑用材；银灰杨和欧美杨的木质素含量低，适于造纸。同地区栽培的毛果杨和胡杨生长速度慢、生长状况欠佳，在生产上不宜采用。生长速度缓慢除了受光合、蒸腾影响外，也可能与激素含量有关，赤霉素含量较高会导致木质部细胞早期分化程度高。毛果杨虽生长缓慢，在我国引种相对较少，但是作为林木树种遗传转化研究中的代表种，意义重大。而胡杨能够抵御干旱盐碱，具有防护作用，这可能与其cis—ABA含量较高、气孔导度低、蒸腾速率低、水分丧失少有关。

英文摘要：

Poplars are widely used in scientific research and forestry production due to their traits of fast growth, strong adaptability, and so on. We chose five poplar species as research object, namely, Populus trichocarpa, P. tomentosa, P. canescens, P. - euramericana and P. euphratica, in order to analyze the differences in seedling growth, photosynthesis, microstructure, lignin components and contents of hormones, for a purpose of providing advice for production. Results showed that P. tomentosa, P. canescens and P. - euramericana were elite poplar species in the planting region. They grow faster than the other two species, presumably because they have higher photosynthetic rate yielding more organic compounds, and greater stomatal conductance with high transpiration rate to transport water and inorganic salt efficiently. It suggests that these three species have greater potential in real production. In addition, P. tomentosa has higher lignin content, which might be suitable to be used as building material; In contrast, P. canescens and P. x euramericana have lower lignin content, which might be suitable to be applied in papermaking industry. P. trichocarpa and P. euphratica grow slowly, suggesting that they are unsuitable for production. In addition to effects of photosynthesis and transpiration, their slow growth may also relate to plant hormones. High contents of gibberellins would lead to high degree of differentiation of xylem ceils in early growth stage. Furthermore, P. trichocarpa also acts as a model tree in forestry genetic transformation which is very important in scientific research. P. euphratica is tolerant to drought and salinity stresses and is important in environmental protection, which might have relationship with high cis-ABA content, low stomatal conductance, low transpiration rate and little water loss.