Populus euphratica forests in river floodplains in southwestern Iran are degraded heavily. Tree plantation is one method by which the restoration of these degraded sites would be possible. Trees are expected to influence soils through different mechanisms such as nutrition and nutrient return. This study was conducted in a randomized block design with three blocks constitute of Populus euphratica, Eucalptus camaldulensis, E. microtheca, Acacia farnesiana, A. salicina, A. saligna, A. stenophylla and Dalbergia sissoo monoculture plantations established in 1992. Soils were sampled in November 2006. Leaf litter fall was collected from the beginning of November 2006 and extended to November 2007 at bi-weekly intervals. The tree species were differend in there influence on soil carbon, N, P, K, Ca and Mg. The two groups (NFTs and non-NFTs) were differend in soil carbon, C:N ratio, K and Mg. Nutrition and nutrient return of the species as the two studied mechanisms could explain the most of the difference between the different species and even between the two groups.
