Soil communities exert strong influences on the processing of organic matter and nutrients. Plantations of trees, especially of nitrogen fixing ones, may affect the soil macrofauna through litter quality and quantity. This study was conducted in a randomized block design with three blocks consisting of Populus euphratica, Eucalyptus camaldulensis, Eucalyptus microtheca, Acacia farnesiana, Acacia salicina, Acacia saligna, Acacia stenophylla and Dalbergia sissoo monoculture plantations that were established in 1992. Soils and soil macrofauna were sampled in November 2006. Leaf litterfall was collected from November 2006 to November 2007 at bi-weekly intervals. Macroinvertebrate abundance and biomass were consistently higher in A. salicina plantations than in the others, whereas they were lowest in E. camaldulensis. Tree species and nitrogen fixing trees significantly influenced the soil macrofauna richness. The results suggest that the earthworm distribution is regulated by leaf litter quality (Ca, C and N) whereas the macrofauna richness is regulated by leaf litter mass, soil organic carbon and leaf litter Mg. Totally, it was revealed that the tree species clearly affected macrofauna whereas nitrogen fixation did not.

Key message This study shows that functional grouping of the species based on nitrogen fixing ability along with initial leaf litter C/P, C/N, P and N could help us predicting leaf litter decomposition rate. Abstract Grouping species into functional groups is a good approach to understanding exotic plants impacts on ecosystem functioning in their new environment. One key plant trait that has large ecosystem-level consequences is the ability of plants to fix atmospheric nitrogen into plant available forms. Most previous studies have reported faster leaf litter decomposition rates of nitrogen fixing than nonnitrogen-fixing species, supporting the separation of these as functional groups. Here, we present a multispecies monitoring of litter decomposability of seven tree species in a 1 year decomposition experiment in outdoor litter bed common garden experiment in river floodplain in South Western Iran. We tested within-and between-functionalgroups for rates of leaf litter decomposition and nutrient dynamics. Our results highlight that nitrogen-fixing trees and non-nitrogen-fixing trees can be distinguished based on specific leaf area and leaf litter traits. The interesting results were that the leaf litter decomposition rates of the two functional groups were related to different initial leaf litter traits. Leaf litter decomposition rates of nitrogenfixing trees were related to initial leaf litter C/P, C/N, N, P and Ca, while leaf litter decomposition rates of non-nitrogen-fixing trees were only related to initial leaf litter Ca. Whereas specific leaf area was the best predictor of leaf litter decomposition rates among all the species. Therefore, our results revealed that both initial leaf litter traits and functional groups were predicting leaf litter decomposition rates.

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.

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