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In this study several same-aged poplar species and clones were selected including Populus deltoides Marsh. CV. "Lux" (P.d "Lux"), Populus deltoides Marsh. CV. "Harvard" (P.d "Harvard"), Populus x canadensis Moench "Triplo" (P.xc "Triplo"), Populus x canadensis Moench "I-45/51" (P.xc "I-45/51"), planted in poplar research station about 20 years ago in the north of Iran, and Populus caspica Bornm. (P. caspica) as endemic and endangered poplar species. Some quantitative characteristics of the trees and soil samples were taken based on completely randomized block design. Samplings of live and senescent leaves were carried out in two-stages, mid-summer during the peak nutritional activities of trees and mid-autumn for senescent leaves. Soil samples were analyzed to determine organic carbon (OC), total nitrogen (N), available phosphorus (P) and exchangeable potassium (K). OC, total of N, P and K were also determined in live and senescent leaves. The results showed that P.d "Harvard" had the highest total height, DBH and diameter of crown compared to the other species and clones. The amount of OC, N and P in soil and live leaves of P.d "Harvard" clone are more than those of the other species and clones. OC, N, P, and K returned by senescent leaves were higher and lower for P.d "Harvard" and P. caspica respectively. P retranslocation for all of the clones and species was higher compared to N and K. The highest retranslocation percentage was observed in P. caspica (N=18.93, P=39.63, K=24.02) and the lowest (N=12.09, P=32.46, K=21.14) in P.d "Harvard" clone. It could be concluded that poplar species and clones have different nutritional requirements and retranslocation capabilities. It appears that P.d "Harvard" clone showed higher quantitative growth it could be beneficial for maintaining the soil nutrient status for successive plantings. [ABSTRACT FROM AUTHOR]