وحید حسینی

Populus Euphratica forests in Dez river floodplains in southwestern Iran are degraded heavily. Tree plantation is one method by which the restoration of these degraded sites would be possible. The capability of each plant to utilize available resources is species specific therefor this factor should be considered. This study was conducted in a randomized block design with three blocks constitue of popullus euphratica, Eucaliptus camaldulensis, E. microthca, Acacia farnesiana, A. salicina, A. stenophlla and Dalbergia sissoo monoculture plantations that were established in 1992. The aim of this study is to distinguish the differences in the degree of internal cyclling of nutrient ( retranslocation ) among these species. Leaf samples were collected from the stands in September 2006. Leaf litter fall was collected from the beginning of November 2006 and extended to November 2007 at bi-weekly intervals. The retranslocation efficiency of Nitrogen, Phosphorus and Potassium were significantly differed between the tree plantations. The Nitrogen retranlocation efficiniency of P.euphratica and A.saligna were significantly higher than other species. This index in the case of Phosphorus was highest in A.saligna, P.euphratica and D.sissoo and lowest in A.salicina, E.camaldulensis and E.microtheca. The potassium retranslocation efficiency of p.euphratica, D.sissoo, A.farnesiana and A.saligna were the highest. Therefore A.saligna and P.euphratica have more internal nutrient recycle and in contrast A.salicina has less. Consequently we might see that the two first species influence soil negatively and the latest positively. Finally it should be implied that nutrient retranslocation is an important factor for species selection.