Differences in chemical composition of needle and leaf litter from exotic and native tree species stands

The potential differentiations in litter chemistry among native and non-native trees are poorly understood. We compared the chemical composition of leaf litterfall of 11 exotic tree species, e.g. coniferous: Abies cephalonica, A. grandis, A. procera, Chamaecyparis pisifera, Pinus peuce, Pseudotsuga menziesii, Thuja plicata, and deciduous: Acer rubrum, A. saccharum, Betula alleghaniensis and Quercus rubra, with that of a native European conifer, Pinus sylvestris (as reference to coniferous species) anda mixture of native European Quercus robur, Carpinus betulus, Tilia cordata, T. platyphyllos and Corylus avellana leaves (as a reference mixture of deciduous species). We found significant differences among the species studied in nitrogen and carbon content in needles/leaves, C/N ratio, as well as total soluble phenolic compounds (TPh) and total nonstructural carbohydrates (TNC) content, including soluble carbohydrates and starch. However, we found no clear differentiation of exotic from native tree species in the analyzed elements and metabolites. Among the exotic coniferous tree species, P. menziesii stood out among the species studied – fallen needles of this species were characterized by relatively high TPh and TNC content. The relationships between TPh and TNC content in leaf and needle litter among tree species were similar among two consecutive years. For deciduous tree species, the tendency of higher TPh content and C/N ratio in leaves falling earlier (September; leaves of sun-type) than later (November; leaves of shade-type) was more distinct than in coniferous tree species. Generally, we cannot see any special differences in the levels or mutual quantitative relationships of the chemical compounds studied in fallen needles/leaves of exotic tree species in comparison with native tree species.