comparison among different clones of populus nigra in aspect of cold resistance

increasing of wood demand is currently one of the most important problems in our society. different clones of populus nigra from salicacea as a native fast-growing species have a good potential for planting in wide scale. but because of the ecological differences in the field, especially. temperature alterations, segregation of the cold resistant clones in relation to in seedling stage establishment is very important. peroxidase enzyme as one of the most sensitive physiological factors to environmental stresses, especially low temperature was used to compare the ability of cold resistance of five clones of this species. quantitative and qualitative activities of this biochemical marker (pod) were studied during five months from september till may. the result indicated that p. nigra 62.231 and 64.13 clones had the best ability of early autumn cold resistance and p. nigra 56.52 clone had the best ability of late spring cold resistance. also, p. nigra 62.171 and 64.13 clones the best winter cold resistance.