Seasonal differences in green leaf breakdown and nutrient content of deciduous and evergreen tree species and grass in a granitic headwater stream

Litter processing was examined in autumn–winter and spring–summer in a second order stream in Galicia (NW Spain). We compared decay rate and nutrient dynamics of green leaves of several deciduous (riparian: Alnus glutinosa, Betula alba and Populus×canadensis; terrestrial: Castanea sativa, Quercus robur), and evergreen tree species (terrestrial: Pinus radiata and Eucalyptus nitens), in addition to ray-grass (Lolium perenne). In the autumn–winter period, the decay rates (−k) ranged between 0.0086 degree-days−1 for poplar, and 0.0019 degree-days−1 for birch leaves. Alder showed the most rapid breakdown in spring–summer (0.0124 degree-days−1), and pine the slowest (0.0016 degree-days−1). Deciduous species exhibited general higher processing rates than evergreen species and ray-grass. The initial nitrogen and phosphorus contents were higher in riparian species leaves and ray-grass, being higher in spring (2.28±0.14% and 0.24±0.04% of nitrogen and phosphorus, respectively) than in autumn (1.88±0.36% of nitrogen and 0.18±0.03% of phosphorus). A significant correlation coefficient was found only between mean nitrogen leaf packs contents during incubation and decay rates (r=0.61; p=0.012).