effect of hydromorphy and drought stresses on net photosynthesis rate and viability for three poplar species

poplars are classified as fast-growing and slightly water tolerant species which will be weakened with decreased growth in extreme moisture or drought lands. the plantation of these species in agricultural lands and at the edge of rivers and water canals has currenthy an important role in both economical and social development of rural regions. the purpose of this study was to investigate and compare the effect of drought and hydromorphy stresses on three species of poplars including populus nigra 64.13, populus deltoides 63.51 and populus euramericana 476. for this purpose, the cuttings of the best clones of the mentioned species as wood production in golestan province were planted in plastic pots. then 30 seedlings of each species for each treatment were carried to the laboratory with the same conditions and were treated with water stress (drought and hydromorphy) and one control (150 milliliters irrigation every two days) as factorial experiment. net photosynthesis rate (npr) was measured daily by lca-3 continuously till the seedlings were completely dead. the variance analysis and duncan multiple comparison of data showed that water stress caused decreasing of npr and viability percentage of the seedlings compared with control condition. populus euramericana was more successful in hydromorphy and drought stresses in comparison with the other species, and also more resistance to hydromorphy than drought stress from the npr and viability point of view. whereas, populus deltoides and populus nigra had more resistance to drought stress than hydromorphy.