Ghasemi-Aghbash F., Hosseini V., Poureza M., 2016. Nutrient dynamics and early decomposition rates of Picea abies needles in combination with Fagus orientalis leaf litter in an exogenous ecosystem. Ann. For. Res. 59(1): 21-32.Abstract. The Hyrcanian forests in the Northern Iran are originally poor of coniferous and are considered as a refugium of temperate broad-leaved trees during the Quaternary glaciations. In this study mass loss and nutrients dynamic of Norway spruce needles when combined with oriental beech litter was investigated in a 50-year plantation of pure Norway spruce in the Hyrcanian forests. The litter bags technique was used to monitor the mass loss and nutrients concentration after 60, 120, 180, 270 and 400 days. The results showed that when decomposed alone the mass loss rate of spruce needles was generally lower than what reported in Europe. However, when combined with oriental beech litter the mass loss rate was hastened compared to when decomposed alone. A positive non-additive effect of beech leaf litter was observed on spruce nutrients dynamic. The concentration of N, P, K, and Mg in combined spruce needles with beech litter was generally higher compared to when spruce needles decomposed alone during decomposition time. While the concentration of Mn and Ca in combined spruce needles with beech litter was generally higher than when spruce needles decomposed alone. At the end of the decomposition period the release of Mn and N was significantly higher in combined spruce needles than when it decomposed alone. Based on the stepwise regression N was the only nutrient entered to model which explained 37% of mass loss variation. It was concluded that oriental beech leaf litter drive a non-additive effect on mass loss and nutrient dynamic of Norway spruce needles. Therefore combining the plantation of Norway spruce with oriental beech can result in better regulating of needles decomposition and nutrients cycle.